Gypsum composition comprising uncooked starch having mid-range viscosity, and methods and products related thereto

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

[0002] Gypsum (calcium sulfate dihydrate) occurs naturally and can be mined in rock form. It can also be in a synthetic form (called "singip" in the art) as a by-product 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 can then be rehydrated to form set gypsum in the desired shape (e.g., as a board). During the manufacture of boards, stucco, water, and other ingredients as needed are typically mixed in a pin mixer (as that term is used in the art). The slurry is formed and discharged from the mixer onto a moving conveyor carrying 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 (a skim coat is optionally included on the paper). Another cover sheet, with or without a skim coat, is applied over the slurry to form a sandwich structure of desired thickness, for example, with a forming plate. The mixture is cast and set to form set (i.e., rehydrate) gypsum by reaction of the calcined gypsum with water to form a matrix of crystalline hydrated gypsum (i.e., calcium sulfate dihydrate). It is the desired hydration of the calcined gypsum that allows for the formation of an interlocking matrix of set gypsum crystals, thereby imparting strength to the gypsum structure in the product. Heat is required (e.g., in a kiln) to remove the remaining free (i.e., unreacted) water to obtain a dry product.

[0003] The excess water that is discharged represents an inefficiency in the system; removing the water requires an energy input and slows down the production process to accommodate drying procedures. However, reducing the amount of water in the system has proven very difficult without compromising other important aspects of the commercial product, including board weight and strength.

[0004] It will be understood that this background description has been made by the inventors to aid the reader and is not to be taken as a reference to the prior art or as an indication that any of the problems presented are themselves understood in the art. While the principles described may, in some respects and embodiments, alleviate problems inherent in other systems, the scope of the protected innovation is defined by the appended claims, rather than by the ability of the claimed invention to solve any particular problem described herein. Summary of the Invention

[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 an embodiment of the invention, uncooked starch of a desired viscosity can be included in a gypsum slurry (along with stucco, water, and other desired additives such as one or more of foam, dispersants, polyphosphates, accelerators, retarders, etc.) to enhance the strength of the resulting product, such as gypsum board (as used herein, such as forms of wallboard including drywall used for interior wall surfaces, ceilings, partitions, etc.). More specifically, the starch has (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 moderate peak viscosity of about 120 BU to about 1000 BU when the viscosity is measured by placing the starch in a slurry containing water at 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 at 75 rpm and 700 cmg. While not wishing to be bound by any particular theory, it is believed that uncooked starches having a viscosity described herein allow the starch molecules to escape from the granules, thereby imparting strength (e.g., comprising an interlocking matrix of set gypsum) to the gypsum composition resulting from the stucco slurry.

[0006] Advantageously, uncooked starch of a desired viscosity according to embodiments of the invention is generally heavier and exhibits less variability and higher bulk density than pregelatinized starch. In this regard, pregelatinized starch may have greater variability in bulk density, which may lead to imprecise feeding of the starch to the stucco slurry. In addition, uncooked starch of a desired viscosity may advantageously allow for less water demand in the gypsum wallboard manufacturing process. For example, uncooked starch of a desired viscosity may reduce the water demand in a stucco slurry by at least about 10% (e.g., at least about 20%) as compared to pregelatinized starch in an otherwise identical stucco slurry.

[0007] Thus, in one aspect, the invention provides a gypsum board. The board includes a set gypsum core disposed between two cover sheets, the core being formed from a slurry including 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 aspect, the invention provides a stucco slurry (sometimes referred to as a "stucco slurry"), the 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, as measured by the HWVA method.

[0009] In another aspect, the present invention provides a method of preparing a gypsum board, the method comprising: a slurry comprising 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, as measured by the HWVA method. The slurry is disposed 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 aspect, the invention provides an acoustical panel comprising an acoustical component including fiber 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 the viscosity is measured by the HWVA method. The panel preferably has a noise reduction factor of at least about 0.5 according to ASTM C 423-02.

[0011] In another aspect, the invention provides a gypsum board. The board includes a set gypsum core disposed between two cover sheets, the core being formed from a slurry including 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. Viscosity is measured by placing the starch in a slurry including water at a starch concentration of 15% solids, using a Viscograph E instrument set at 75 rpm and 700 cmg, where 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 maximum viscosity is recorded as the peak viscosity.

[0012] In another aspect, the invention provides another gypsum board comprising a set gypsum core disposed between two cover sheets, the core being formed from a slurry including stucco, water, and at least one uncooked starch, the at least one uncooked starch having a cold water viscosity of about 1 centipoise to about 50 centipoise at 10% solids in water when the viscosity is measured at 25° C. by the Brookfield Viscometer Method.

[0013] In another aspect, the invention provides a stucco slurry (sometimes referred to as a "stucco slurry"), the 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, as measured by placing the starch in a slurry with water at 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 at 75 rpm and 700 cmg.

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

[0015] In another aspect, the present invention provides a method for preparing a gypsum board. The method includes 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, as measured by using a Viscograph E instrument set at 75 rpm and 700 cmg, placing the starch in a slurry comprising water at 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. The slurry is disposed 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 aspect, the invention provides a method of preparing a gypsum board. The method includes 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 centipoise to about 50 centipoise at 10% solids in water when the viscosity is measured at 25° C. by the Brookfield Viscometer method. The slurry is disposed 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 aspect, the invention provides an acoustical panel comprising an acoustical component including fibers 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 by placing the starch in a slurry including water at 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 at 75 rpm and 700 cmg. The panel preferably has a noise reduction factor of at least about 0.5 according to ASTM C 423-02.

[0018] In another aspect, the invention provides an acoustical panel comprising an acoustical component including fiber and at least one uncooked starch, wherein the at least one uncooked starch has a cold water viscosity of about 1 centipoise to about 50 centipoise at 10% solids in water when viscosity is measured by the Brookfield Viscometer method at 25° C. The panel preferably has a noise reduction factor of at least about 0.5 according to ASTM C 423-02. [Brief description of the drawings]

[0019] [Figure 1] FIG. 2 is a Brabender amylogram of a 15% starch slurry in water according to an embodiment of the invention as described in Example 1, illustrating the viscosity of the starch, where the X-axis is time and the Y-axis overlays viscosity (primary Y-axis on the left) and temperature (secondary Y-axis on the right). [Diagram 2] 1 is a bar graph of the wet compressive strength of set gypsum compositions formed from a slurry containing uncooked, acid-modified corn starch B compared to set gypsum compositions formed from slurries containing pregelatinized corn starches A and B, respectively, at intervals of 3, 5, 7, and 10 minutes, as described in Example 2. [Diagram 3]1 is a graph of the drying rate (weight vs. time) at 450° F. of a board formed from a slurry containing uncooked starch compared to a board formed from a slurry containing pregelatinized corn starch B, as described in Example 3. [Figure 4] FIG. 2 is a Brabender amylogram of a 15% starch slurry in water illustrating the hot water viscosity assay (HWVA) of starch according to an embodiment of the invention, where the X-axis is time and the Y-axis overlays viscosity (primary Y-axis on the left) and temperature (secondary Y-axis on the right). [Diagram 5] FIG. 2 is a Brabender amylogram of a 15% starch slurry in water illustrating the hot water viscosity assay (HWVA) of acid modified tapioca, wheat, and potato starches according to an embodiment of the invention, with the X-axis being time and the Y-axis overlaid with viscosity (primary Y-axis on the left) and temperature (secondary Y-axis on the right). [Figure 6] FIG. 13 is an illustration illustrating a board product with the cover sheet pulled back to reveal a defect (blister) in the board core, as discussed in Example 9 herein. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] An embodiment of the invention is predicated, at least in part, on the inclusion of uncooked starch in a stucco slurry (sometimes referred to as a "gypsum slurry") to enhance the strength of the resulting board having one or more gypsum layers formed from the gypsum slurry. In one aspect, 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 aspects, the uncooked starch is characterized as having a "medium" peak viscosity (e.g., about 120 Brabender units to about 1000 Brabender units measured according to the methods described herein). It will be understood that although viscosity characteristics are determined when the starch is subjected to certain conditions according to the viscosity measurement methodology described herein, it is not necessary to add uncooked starch to the slurry under these conditions. Although small chain migratory starches have been used to enhance the core bond of paper, the traditional use of non-migratory uncooked starch has been undesirable in gypsum slurries because core strength was not significantly improved. Embodiments of the present invention unexpectedly overcome this shortcoming.

[0021] Surprisingly, it has been found that starches having a desired hot water viscosity are effective for use in gypsum slurries to enhance the strength of the resulting board product. As described herein, selecting a moderate hot water viscosity for use in gypsum (stucco) slurries, i.e., about 20 BU to about 300 BU according to the HWVA method, surprisingly results in a 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 in which corn starch is used, the peak viscosity discussed herein can be used to correlate the molecular size. In this regard, it has been found that the peak viscosity effectively correlates with the molecular size of the corn starch and thus the board strength. While not wishing to be bound by any particular theory, it is surprising that 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, wheat starch may have a larger molecular size at lower peak viscosity than corn starch with higher peak viscosity. Thus, it has been surprisingly and unexpectedly found that hot water viscosity has a better correlation with molecular size across starches. However, if desired, the peak viscosity described herein can be used when evaluating a single starch.

[0022] The inclusion of uncooked starch according to the invention has been found to provide benefits, for example, consistent with some embodiments, with respect to starch efficiency (e.g., allowing less starch to be used), improved product strength, and water demand. According to embodiments of the invention, the benefits, including those with respect to starch efficiency, water demand, and / or strength, represent significant improvements and advances over non-gelatinized starches (uncooked) having hot water viscosities below 20 BU or above 300 BU, and / or peak viscosities below 120 BU or above 1000 BU. Additionally, in some embodiments, it has been surprisingly and unexpectedly found that the drying rate of slurries containing uncooked starch is similar to the drying rate of slurries containing pregelatinized starch. This is particularly surprising since uncooked starch needs to absorb extra heat energy to gelatinize the starch. These findings provide numerous benefits, including, but not limited to, reduced raw material costs, improved manufacturing efficiency, improved product strength, and the like, allowing, for example, lighter weight products with sufficient strength properties.

[0023] Uncooked starch according to the invention can be included in a stucco slurry to form a gypsum layer in a board in embodiments of the invention, and can be used with a gypsum board layer (e.g., core) optionally having a skim coat on one or both major sides of the core. In some embodiments, board cores formed from stucco slurries containing uncooked starch can have a thickening layer on one or both major sides of the core, as described in commonly assigned, co-pending U.S. patent application Ser. Nos. 15 / 186,176, 15 / 186,212, 15 / 186,232, and 15 / 186,257, the thickening layer arrangements of which are incorporated herein by reference.

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

[0025] The starch is uncooked according to an embodiment of the present invention. Uncooked starch is characterized by being cold water insoluble and having a semi-crystalline structure. Typically, uncooked starch is obtained by wet milling and is not modified by heating wet starch as in the case of cooked starch. It should be noted that the uncooked starch according to the present invention is different from cooked starch, which is characterized by being cold water soluble 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, co-pending U.S. patent applications 14 / 494,547, 14 / 044,582, and 13 / 835,002. Cooked starch is sometimes referred to as pregelatinized starch, since the crystalline structure of the starch granules melts, resulting in starch gelatinization, characterized by the disappearance of birefringence under a microscope using polarized light.

[0026] Preferred uncooked starches are different from acid-modified mobile starches used in the art for the enhancement of paper-core bonding as they do not provide the same strength properties and migrate to the paper-core interface due to their small chain length. Acid-modified mobile starches have a minimum molecular weight, typically less than about 6,000 Daltons. Preferred uncooked starches according to embodiments of the invention have a higher molecular weight than mobile starches, for example at least about 15,000 Daltons. The average molecular weight is indicated by the hot water viscosity. Preferred uncooked starches have 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 that found in pregelatinized starch. This is surprisingly useful, for example, because the consistent density allows a volumetric feeder to add starch more accurately and consistently. For example, in some embodiments, the bulk density can be about 35 pcf to about 50 pcf, about 35 pcf to about 45 pcf, about 37 pcf to about 50 pcf, about 37 pcf to about 45 pcf, about 40 pcf to about 50 pcf, about 40 pcf to about 47 pcf, about 40 pcf to about 45 pcf, or about 41 pcf to about 45 pcf.

[0028] In contrast to uncooked starch according to the 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 and the starch molecules are dissolved in water, resulting in a good dispersion. When converting starch granules to gelatinized form, it is found that initially the starch granules give little viscosity in water, since the starch granules are water insoluble. As the temperature increases, the starch granules swell and the crystalline structure melts at the gelatinization temperature. The peak viscosity is reached when the starch granules have maximum swelling. Further heating breaks down the starch granules and dissolves the starch molecules in water, resulting in a sharp drop in viscosity. After cooling, the starch molecules reassociate to form a 3D gel structure, which increases the viscosity.

[0029] Uncooked starch according to embodiments of the invention is typically in a native granular form. According to some embodiments of the invention, the granular uncooked form may undergo at least some gelatinization during gypsum wallboard production (e.g., in a kiln).

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

[0031] Uncooked starch exhibiting the viscosity characteristics according to the present invention provides significant advantages in the strength of products (e.g., wallboard). Because starch contains glucose monomers with three hydroxyl groups, starch provides many sites for hydrogen bonding to the gypsum crystals. Without wishing to be bound by any particular theory, it is believed that the molecular size of uncooked starch exhibiting hot water viscosity characteristics allows optimal mobility of the starch molecules, aligning them with the gypsum crystals to promote good binding of starch to the gypsum crystals, for example, via hydrogen bonding, strengthening the resulting crystalline gypsum matrix. Uncooked starches with viscosities outside the desired hot water viscosity range, either with longer chain lengths and higher molecular weights (too high viscosity) and shorter chain lengths and lower molecular weights (too low viscosity), respectively, do not provide the same combination of benefits. Thus, optimal binding of gypsum crystals with uncooked starch molecules of the desired hot water viscosity effectively improves the strength of the crystalline gypsum matrix and requires less starch to promote its strength compared to conventional starches. Uncooked starch surprisingly and unexpectedly reduces the water demand of the gypsum slurry due to the surprisingly high fluidity of the stucco slurry containing uncooked starch.

[0032] The uncooked starch added to the gypsum (stucco) slurry desirably has a medium molecular weight as indicated by a hot water viscosity of about 20 BU to about 300 BU. The medium hot water viscosity of the uncooked starch is determined according to the HWVA method described herein. The medium peak viscosity is measured in the following manner. Brabender peak viscosity is measured using a Viscograph E (CW Brabender) set at 75 rpm and 700 cmg. The starch is slurried at 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 before being cooled 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 the uncooked starch is generally greater than 20 BU, such as from about 20 BU to about 300 BU, e.g., from about 20 BU to about 280 BU, from about 20 BU to about 250 BU, from about 20 BU to about 200 BU, from about 20 BU to about 175 BU, from about 20 BU to about 150 BU, from about 20 BU to about 125 BU, from about 20 BU to about 100 BU, from about 20 BU to about 75 BU, from about 20 BU to about 50 BU, from about 30 BU to about 300 BU, from about 30 BU to about 280 BU, from about 30 BU to about 250 BU, from about 30 BU to about 150 BU, from about 30 BU to about 125 BU, from about 30 BU to about 100 BU, from about 30 BU to about 75 BU, from about It may be 30BU to about 50BU, about 50BU to about 300BU, about 50BU to about 280BU, about 50BU to about 250BU, about 50BU to about 200BU, about 50BU to about 150BU, about 50BU to about 100BU, about 100BU to about 300BU, about 100BU to about 280BU, about 100BU to about 250BU, about 100BU to about 200BU, about 100BU to about 150BU, about 150BU to about 300BU, about 150BU to about 280BU, about 150BU to about 250BU, about 150BU to about 200BU, about 200BU to about 300BU, or about 200BU to about 280BU.

[0034] In some embodiments, the starch has a peak viscosity of at least about 100 Brabender units, and is from about 120 Brabender units to about 1000 Brabender units, e.g., from about 120 Brabender units to about 875 Brabender units, from about 120 Brabender units to about 850 Brabender units, from about 120 Brabender units to about 700 Brabender units, from about 120 Brabender units to about 550 Brabender units, from about 120 Brabender units to about 460 Brabender units, from about 120 Brabender units to about 300 Brabender units, from about 150 Brabender units to about 1000 Brabender units, from about 150 Brabender units to about 850 Brabender units, from about 150 Brabender units to about 750 Brabender units, from about 150 Brabender units to about 500 Brabender units, from about 150 Brabender units to about 500 Brabender units, from about 150 Brabender units to about 600 Brabender units, from about 150 Brabender units to about 700 Brabender units, from about 150 Brabender units to about 850 Brabender units, from about 150 Brabender units to about 850 Brabender units, from about 150 Brabender units to about 75 ... The number of units may be from about lavender units to about 300 Brabender units, from about 250 Brabender units to about 850 Brabender units, from about 250 Brabender units to about 600 Brabender units, from about 250 Brabender units to about 500 Brabender units, from about 300 Brabender units to about 875 Brabender units, from about 350 Brabender units to about 800 Brabender units, from about 350 Brabender units to about 750 Brabender units, from about 400 Brabender units to about 1000 Brabender units, from about 400 Brabender units to about 875 Brabender units, from about 400 Brabender units to about 700 Brabender units, from about 500 Brabender units to about 850 Brabender units, from about 500 Brabender units to about 700 Brabender units, from about 600 Brabender units to about 1000 Brabender units, etc.

[0035] Properties of uncooked starch include having a low viscosity in cold water (i.e., at a temperature of 77° F. (25° C.)) whereas properties of pregelatinized starch include having an instantaneous high viscosity in cold water. Uncooked starches according to the present disclosure preferably have a cold water viscosity in cold water of less than about 50 centipoise, e.g., about 40 centipoise or less, about 30 centipoise or less, about 20 centipoise or less, or about 10 centipoise or less (e.g., from about 1 centipoise to about 50 centipoise, from about 1 centipoise to about 40 centipoise, from about 1 centipoise to about 30 centipoise, from about 1 centipoise to about 20 centipoise, from about 1 centipoise to about 10 centipoise, from about 5 centipoise to about 50 centipoise, from about 5 centipoise to about 30 centipoise, from about 5 centipoise to about 20 centipoise, from about 3 centipoise to about 15 centipoise, from about 3 centipoise to about 10 centipoise, from about 3 centipoise to about 7 centipoise, etc.). Cold water viscosity is measured according to the Brookfield Viscometer method with the following test profile: Add starch (20 g, dry) to water (180 g) in a Waring blender (Model 31BL92) while mixing at low speed for 15 seconds. Transfer starch solution (200 g) to a measuring cup. Select paddle #2 and 60 RPM. The viscosity value measured at 20 seconds is used as the viscosity of the starch.

[0036] Uncooked starches according to embodiments of the present invention are advantageously easy to mix with water because of their low viscosity in water. In contrast, pregelatinized starches can undesirably cause "fish eyes", a condition characterized by one or more large lumps forming in an aqueous solution during mixing. Without wishing to be bound by any particular theory, it is believed that during the mixing process, the large lumps are caused by the rapid absorption of water by the starch, forming a viscous film on the surface of the lumps that prevents the penetration of water through the lumps. Uncooked starches are believed to avoid the fish eye condition due to their cold water insolubility, which results in the separation of the starch granules.

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

[0038] The stucco slurry is typically formed in a pin 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 premixed prior to entering the mixer, such as one or more dry raw materials and / or one or more wet raw materials. By "adding to the slurry" as used herein, it will be understood that the raw materials may be premixed in any suitable manner prior to entering the mixer where the gypsum (stucco) slurry is formed as described herein.

[0039] The uncooked starch of the desired hot water and / or peak viscosity characteristics characteristic of this invention can be included in the stucco slurry in wet or dry form. If in wet form, the starch can be included at any suitable concentration and can be premixed with the other wet ingredients.

[0040] As used herein, uncooked means that the starch has a degree of gelatinization of less than about 5% (e.g., less than about 1%, such as less than about 3%, or zero) prior to inclusion in the stucco slurry. In some embodiments, uncooked starch may become partially or fully gelatinized when exposed to high temperatures in the gypsum wallboard manufacturing process, e.g., in a kiln during a drying procedure to remove excess moisture.

[0041] Uncooked starch having hot water and / or peak viscosity characteristics according to embodiments of the invention can surprisingly and unexpectedly be included in the slurry in relatively small amounts (solids / solids basis) and still achieve significant strength improvements in the board. Thus, in preferred embodiments of the invention, the uncooked starch having hot water and / or peak viscosity characteristics is included in the stucco slurry in an amount of about 5% or less by weight of the stucco (e.g., about 1% to about 4%), such as about 2% or less by weight of the stucco. For example, the uncooked starch can be included in an amount of 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%, about 1% to about 2%, about 1.5% to about 2%, etc.

[0042] Uncooked starches having desired hot water and / or peak viscosity characteristics can be combined with other starches according to embodiments of the invention. For example, uncooked starches exhibiting desired viscosity characteristics can be combined with other starches to enhance both core strength and paper-core bonding, especially if increased water demand is tolerated. Thus, in some embodiments of the invention, the stucco slurry can include one or more uncooked starches having hot water and / or peak viscosity characteristics, as well as one or more other types of starches. The other starches can include, for example, pregelatinized starches. Examples include pregelatinized corn starches 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 can also be in the form of non-gelatinized starches, such as, for example, mobile acid-modified starches, as well as non-gelatinized alkylated starches, such as ethylated starches, having a hot water viscosity of less than about 20 BU or more than 300 BU, or having a peak viscosity of less than 120 Brabender units or more than 1000 Brabender units. Combinations of starches can be premixed (e.g., in a dry mix, optionally with other components such as stucco, or in a wet mix with other wet ingredients) prior to addition to the gypsum slurry, or can be included one at a time in the gypsum slurry, 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 desired hot water and / or peak viscosity properties as a percentage of the total starch content added to the stucco slurry can be, for example, at least about 10% by weight, e.g., 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 therebetween.In exemplary embodiments, the ratio of uncooked starch having the desired hot water and / or peak viscosity characteristics to other starches can be about 25:75, about 30:70, about 35:65, about 50:50, about 65:35, about 70:30, about 75:25, and the like.

[0043] In addition to the starch component, the slurry is formulated to include water, stucco, a foaming agent (sometimes simply referred to as "foam"), and other additives as needed. The stucco can 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 can be fibrous or non-fibrous. A foaming agent can be included to create an air void distribution within the continuous crystalline matrix of the set gypsum. In some embodiments, the foaming agent includes a major weight portion of an unstable component and a minor weight portion of a stable component (e.g., when unstable and stable / unstable blends are combined). The weight ratio of unstable component to stable component is effective to create an air void distribution within the set gypsum core. See, for example, U.S. Patent Nos. 5,643,510, 6,342,284, and 6,632,550. It has been found that suitable void distribution and wall thickness (independently) can be effective in enhancing strength, especially in lower density boards (e.g., less than about 35 pcf). See, for example, US2007 / 0048490 and US2008 / 0090068. In general, evaporation water voids, having voids of about 5 μm or less in diameter, also contribute to the total void distribution along with the air (bubble) voids mentioned above. In some embodiments, the volume ratio of voids having a pore size of greater than about 5 microns to voids having a pore size of about 5 microns or less is about 0.5:1 to about 9:1, e.g., about 0.7:1 to about 9:1, about 0.8:1 to about 9:1, about 1.4:1 to about 9:1, about 1.8:1 to about 9:1, about 2.3:1 to about 9:1, about 0.7:1 to about 6:1, about 1.4:1 to about 6:1, about 1.8:1 to about 6:1, about 0.7:1 to about 4:1, about 1.4:1 to about 4:1, about 1.8:1 to about 4:1, about 0.5:1 to about 2.3:1, about 0.7:1 to about 2.3:1, about 0.8:1 to about 2.3:1, about 1.4:1 to about 2.3:1, about 1.8:1 to about 2.3:1, etc.In some embodiments, the foaming agent is present in the slurry in an amount, for example, less than about 0.5% by weight of the stucco, e.g., from about 0.01% to about 0.5%, from about 0.01% to about 0.4%, from about 0.01% to about 0.3%, from about 0.01% to about 0.2%, from about 0.01% to about 0.1%, 0.02% to about 0.4%, from about 0.02% to about 0.3%, from about 0.02% to about 0.2%, etc.

[0044] Additives such as accelerators (e.g., wet gypsum accelerators, heat resistant accelerators, and weather stabilizing accelerators) and retarders are well known and can 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, for example, blistering and delamination of the core-cover sheet bond, before draining the excess water in the kiln. The hydration rate can be measured in minutes in terms of the time required to reach 50% hydration (simply referred to as "50% hydration"). In accordance with a preferred embodiment, it has been found that a desired 50% hydration time is selected to effectively cut the ribbon of set stucco slurry into desired segments with a knife before the segments enter the kiln and are then further processed to form a board of its final dimensions, avoiding defects such as blistering, delamination, etc. Surprisingly and unexpectedly, by adjusting the hydration rate (e.g., by matching the amount of accelerator and / or retarder in the stucco slurry), the occurrence of board defects such as blistering, delamination, delamination, and / or poor bonding between the gypsum layer and the cover sheet of the board can be reduced or avoided. Without wishing to be bound by a particular theory, uncooked starch does not contain as many contaminants as found in pregelatinized starch. The lower contaminant content of uncooked starch results in less of a retarding effect on the stucco setting process during the preparation of the board. Without wishing to be bound by any particular theory, if the hydration rate is too fast, the board becomes more susceptible to certain defects such as spalling, blistering, etc. It has been found that, because uncooked starch provides less of a retarding effect than is provided by pregelatinized starch, less accelerator must be used in the stucco slurry when uncooked starch is used.

[0046] As will be appreciated by those skilled in the art, the exact amount of accelerator will vary 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 by any suitable amount depending on the circumstances of a particular facility. In some embodiments, the amount of accelerator can be reduced by up to about 40% in a stucco slurry containing uncooked starch compared to the amount of accelerator used in an otherwise identical stucco slurry containing pregelatinized starch. For example, the amount of accelerator may be from about 1% to about 40%, e.g., from about 1% to about 35%, from about 1% to about 30%, from about 1% to about 25%, from about 1% to about 23%, from about 1% to about 20%, from about 1% to about 15%, from about 5% to about 40%, from about 5% to about 35%, from about 5% to about 30%, from about 5% to about 25%, from about 5% to about 23%, from about 5% to about 5% in a stucco slurry containing uncooked starch (compared to the same slurry using pregelatinized starch instead of uncooked starch). The amount can be reduced by about 20%, about 5% to about 15%, about 10% to about 40%, about 10% to about 35%, about 10% to about 30%, about 10% to about 25%, about 10% to about 23%, about 10% to about 20%, about 10% to about 15%, about 15% to about 40%, about 15% to about 35%, about 15% to about 30%, about 15% to about 25%, about 15% to about 20%, about 20% to about 40%, about 20% to about 35%, about 20% to about 30%, and about 20% to about 25%.

[0047] As will be appreciated by those skilled in the art, the amount of accelerator and / or retarder used to achieve such desired hydration rates will vary due to different manufacturing conditions (e.g., purity and quality of gypsum, which may vary in different manufacturing or research facilities, etc.) In some embodiments, the accelerator (e.g., 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, e.g., about 1% to about 2% by weight.

[0048] In some embodiments in which an accelerator and / or retarder are included, the accelerator and / or retarder may each be present in the gypsum slurry in an amount, e.g., from about 0% to about 5% by weight of the stucco (e.g., from about 0.1% to about 3% by weight), e.g., from about 0% to about 1% by weight of the stucco (e.g., from about 0.01% to about 0.08% by weight), on a solids basis. Other additives may be included as needed, e.g., to impart strength to allow for a lighter weight product with sufficient strength, to avoid permanent deformation, to promote green strength, e.g., as the product sets on the conveyor moving down the manufacturing line, to promote fire resistance, to promote water resistance, etc.

[0049] For example, the slurry may, in some embodiments, optionally include at least one dispersing agent to enhance flowability. As with the starch and other ingredients, the dispersing agent may be included in the core slurry in dry form with other dry ingredients and / or in liquid form with other liquid ingredients. 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 polyelectrolyte polymers that are by-products from the production of wood pulp using sulfite cooking. One example of a lignin useful in the practice of the principles of embodiments of the present 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, lower water demand than higher molecular weight dispersants. Thus, 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 retardation than dispersants having a molecular weight 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, although other aqueous solutions ranging from, for example, about 35% to about 55% solids by weight are also readily available. The naphthalene sulfonate may be used in dry solid or powder form, such as, for example, LOMAR D available from GEO Specialty Chemicals. Another exemplary naphthalene sulfonate is DAXAD available from Hampshire Chemical Corp.

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

[0053] If necessary, one or more phosphate-containing compounds can be optionally included in the slurry.For example, in some embodiments, the effective phosphate-containing components include water-soluble components, and can be in the form of ions, salts, or acids, i.e., condensed phosphoric acids, each of which includes two or more phosphoric acid units; condensed phosphate salts or ions (each of which includes two or more phosphate units); and orthophosphate monobasic salts or monovalent ions, and water-soluble cyclic polyphosphate salts.For example, see U.S. Patent Nos. 6,342,284, 6,632,550, 6,815,049, and 6,822,033.

[0054] Phosphate compositions, including phosphate-containing components according to some embodiments of the present invention, can enhance green strength, resistance to permanent deformation (e.g., sagging), dimensional stability, and the like. For example, trimetaphosphate compounds can be used, including sodium trimetaphosphate, potassium trimetaphosphate, lithium trimetaphosphate, and ammonium trimetaphosphate. Sodium trimetaphosphate (STMP) is preferred, but other suitable compounds include, for example, sodium tetrametaphosphate, having about 6 to about 27 repeating phosphate units and having the molecular formula Na n+2 P n O 3n+1 (wherein n=6-27), sodium hexametaphosphate having the molecular formula K4P2O7, tetrapotassium pyrophosphate having the molecular formula Na3K2P3O 10 Dipotassium tripolyphosphate, with the molecular formula Na5P3O 10 sodium tripolyphosphate having the molecular formula Na4P2O7, tetrasodium pyrophosphate having the molecular formula Na4P2O7, aluminum trimetaphosphate having the molecular formula Al(PO3)3, sodium acid pyrophosphate having the molecular formula Na2H2P2O7, sodium tripolyphosphate having 1,000 to 3,000 repeating phosphate units and the molecular formula (NH4 n+2 P n O 3n+1 (wherein n=1,000-3,000), or ammonium polyphosphate having two or more repeating phosphate units and the molecular formula H n+2 P n O 3n+1Other phosphate salts may be suitable, including polyphosphates having the formula: where n is 2 or greater.

[0055] The phosphate may be included in dry or aqueous form (e.g., about a 5% to about 20% phosphate solution, e.g., about a 10% solution). If included, the phosphate may be in any suitable amount (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] Additives suitable for fire and / or water resistant products may also be included, including, for example, siloxanes (water resistant); fibers; heat sink additives such as aluminum trihydrite (ATH), magnesium hydroxide, and / or high expansion particles (e.g., capable of expanding to about 300% or more of its original volume when heated at 1560° F. for about 1 hour). See, for example, co-pending, commonly assigned U.S. Application No. 13 / 400,010, filed February 17, 2012, for a description of these and other ingredients. In some embodiments, high expansion vermiculite is included, although other fire resistant materials may be included. Boards of any fire-resistant related products according to the present disclosure may have an insulation index (TI) of about 17 minutes or more, e.g., about 20 minutes or more, about 30 minutes or more, about 45 minutes or more, about 60 minutes or more, etc., and / or a high temperature shrinkage (at a temperature of about 1560°F (850°C)) of less than about 10% in the xy directions, and an expansion in the z direction of at least about 2%, e.g., at least about 5%, at least about 10%, at least about 15%, or at least about 20%. The fire or water resistant additive may be included in any suitable amount desired, depending, for example, on the fire rating, etc. For example, the fire or water resistant additive, if included, may be in an amount of about 0.5% to about 10% by weight of the stucco, e.g., 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] When included, the siloxane is preferably added in the form of an emulsion. The slurry is then cast and dried under conditions that promote polymerization of the siloxane to form a highly crosslinked silicone resin. A catalyst that promotes polymerization of the siloxane to form a highly crosslinked silicone resin may be added to the gypsum slurry. In some embodiments, a solvent-free methylhydrogen siloxane fluid sold by Wacker-Chemie GmbH (Munich, Germany) under the name SILRES BS 94 may be used as the siloxane. This product is a siloxane fluid that does not contain water or solvent. In some embodiments, it is contemplated that about 0.3% to about 1.0% of BS 94 siloxane may be used, based on the weight of the dry raw material. For example, in some embodiments, it is preferred to use about 0.4% to about 0.8% of the siloxane, based on the dry stucco weight.

[0058] The slurry formulation can be made with any suitable water / stucco ratio, for example, from about 0.4 to about 1.3. However, because the uncooked starches having hot hydrous and / or peak viscosity characteristics of the present invention reduce the amount of water that needs to be added to the slurry to condition the starch compared to other starches, the slurry can be formulated in some embodiments with lower water / stucco ratio inputs than are conventional for other starch-containing gypsum slurries, particularly at low weight / density. For example, in some embodiments, the water / stucco ratio can be from about 0.4 to about 1.2, from about 0.4 to about 1.1, from about 0.4 to about 1, from about 0.4 to about 0.9, from about 0.4 to about 0.85, from about 0.45 to about 0.85, from about 0.55 to about 0.8, from about 0.6 to about 0.9, from about 0.6 to about 0.85, from about 0.6 to about 0.8, and the like.

[0059] The cover sheet may be formed of any suitable material and basis weight. Beneficially, board cores formed from slurries including uncooked starch characterized by hot water viscosity and / or peak viscosity provide sufficient strength in some embodiments, even for lighter weight boards (e.g., having a density of about 35 pcf or less), e.g., in boards having lower basis weight cover sheets, such as less than 45 lbs / MSF (e.g., about 33 lbs / MSF to 45 lbs / MSF). However, if desired, heavier basis weights may be used in some embodiments, e.g., to further increase nail pull resistance or to enhance handling, e.g., to promote desirable "feel" properties for the end user. In some embodiments, to increase strength, especially in lower density boards, one or both of the cover sheets may be formed from paper and may have a basis weight of, for example, at least about 45 lbs / MSF (e.g., from about 45 lbs / MSF to about 65 lbs / MSF, from about 45 lbs / MSF to about 60 lbs / MSF, from about 45 lbs / MSF to about 55 lbs / MSF, from about 50 lbs / MSF to about 65 lbs / MSF, from about 50 lbs / MSF to about 60 lbs / MSF, etc.). Optionally, in some embodiments, one cover sheet (e.g., the "front" paper side when installed) can have a higher basis weight as described above, e.g., to enhance nail pull resistance and handling, and the other cover sheet (e.g., the "back" sheet when the board is installed) can have a slightly lower basis weight, if desired (e.g., less than about 45 lbs / MSF, e.g., from about 33 lbs / MSF to about 45 lbs / MSF (e.g., from about 33 lbs / MSF to about 40 lbs / MSF).

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

[0061] Uncooked starches with the desired hot water and / or peak viscosity characteristics of the present invention provide strength enhancement to products according to the present invention, which may be particularly beneficial at lower weights / densities. For example, in some embodiments, board cores or other slurries cast according to the 2-inch cube test (no bubbles), as described in U.S. Patent Application Publication No. 2014 / 0113124, preferably exhibit a compressive strength of at least about 1100 psi, e.g., 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, etc. Such wet compressive strengths are desirable, for example, to reduce or prevent damage during manufacturing procedures prior to drying the board in a kiln. In addition, boards according to some embodiments of the present invention have good wet compressive strength (e.g., better than boards formed from slurries including pregelatinized starch). For example, in some embodiments, the boards may have a wet compressive strength of at least about 150 psi (e.g., at least about 170 psi) 3 minutes after the start of casting (e.g., when the slurry is deposited on the paper at the production line), at least about 460 psi (e.g., at least about 500 psi or at least about 520 psi) 5 minutes after the start of casting, greater than 580 psi after about 7 minutes after casting, and / or at least about 590 psi after 10 minutes after casting.

[0062] In some embodiments, boards according to the present invention meet the test protocol according to ASTM Standard C473-10, Method B. For example, in some embodiments, when the board is cast at a thickness of ½ inch, the board has a nail pull 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 ASTM C 473, Method B. With respect to flexural strength, in some embodiments, when cast at a thickness of ½ inch, the board has a flexural strength in the machine direction of at least about 36 lb (e.g., at least about 38 lb, at least about 40 lb, etc.) and / or at least about 107 lb (e.g., at least about 110 lb, at least about 112 lb, etc.) as determined according to ASTM Standard C473. Additionally, in some embodiments, the board may have an average core hardness of at least about 11 lbs as determined according to ASTM C-473-10, Method B. These specifications may also be met for the lower density boards described herein (eg, about 35 pcf or less), due at least in part to the hot water viscosity and / or peak viscosity characteristics of embodiments of the present invention.

[0063] Products according to embodiments of the present disclosure may be made on a typical manufacturing 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, for gypsum board, the process typically involves discharging a cover sheet onto a moving conveyor. This cover sheet is the "face" cover sheet in such embodiments, since gypsum board is usually formed "face down".

[0064] Dry and / or wet components of the gypsum slurry are fed into a mixer (e.g., a pin mixer) where they are agitated to form the gypsum slurry. The mixer comprises a body and a discharge conduit (e.g., a gate-canister-boot arrangement known in the art or an arrangement described in U.S. Pat. Nos. 6,494,609 and 6,874,930). In some embodiments, the discharge conduit can include a slurry distributor having either a single inlet or multiple inlets, 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 those embodiments, by using a slurry distributor with multiple feed ports, the discharge conduit may include a suitable flow divider, such as that described in U.S. Patent Application Publication No. 2012 / 0170403 A1. Foaming agent may be added in the discharge conduit (e.g., in the gate described in U.S. Patent Nos. 5,683,635 and 6,494,609) or in the body of the mixer, as needed. The slurry discharged from the discharge conduit after all ingredients, including foaming agent, have been added is the primary gypsum slurry and will form the board core. This board core slurry is discharged onto the 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. A hard edge, as known in the art, may also be formed, for example, from the same slurry stream that forms the front skim coat. In an embodiment in which foam is inserted into the discharge conduit, a secondary gypsum slurry stream may be removed from the mixer body to form a dense skim coat slurry, which may then be used to form the front skim coat and hard edge, as 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 optionally split across the front cover sheet (optionally with 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 a secondary (high density) gypsum slurry that is the same or different from the front skim coat. The cover sheet may be formed from paper, fiber mat, or other types of materials (e.g., foil, plastic, glass mat, nonwoven materials such as blends of cellulose and inorganic fillers, etc.).

[0066] The wet assembly thus provided is conveyed to a forming station where the product is sized (e.g., via a forming plate) to the desired thickness, and to one or more knife sections where it is cut to the desired length. The wet assembly is allowed to set to form an interlocking crystalline matrix of set 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 voids or air pockets from the deposited slurry. Each of the above procedures, as well as processes and equipment for carrying out such procedures, are known in the art.

[0067] The uncooked starches characterized by hot water and / or peak viscosity of the present invention can be used in the formulation of various products, such as, for example, gypsum cellulosic fiber products, such as gypsum wallboard, acoustical (e.g., ceiling) tiles, gypsum-wood fiber wallboard, etc. In some embodiments, such products can be formed from slurries according to embodiments of the present disclosure.

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

[0069] In addition, the gypsum-cellulose product may be in the form of a cellulose host particle (e.g., wood fiber), gypsum, hot water and / or uncooked starch at peak viscosity, and optionally other ingredients (e.g., water-resistant additives such as siloxanes). Other ingredients and methods of manufacture are discussed, for example, in U.S. Patent Nos. 4,328,178, 4,239,716, 4,392,896, 4,645,548, 5,320,677, 5,817,262, and 7,413,603.

[0070] The 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 acoustical panels (e.g., ceiling tiles). The starch can be mixed with plaster of Paris, water, and other ingredients as desired in some embodiments. However, the uncooked starch with hot water and / or peak viscosity according to some embodiments is not limited to use with plaster of Paris. The uncooked starch with hot water and / or peak viscosity according to some embodiments can provide good bonding between the starch and non-setting components such as fibers (e.g., mineral wool, etc.). In some embodiments, the panel has a noise reduction factor according to ASTM C 423-02 of at least about 0.5 (e.g., at least about 0.7 or at least about 1). For a discussion of the materials and manufacturing methods for acoustical 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 the following embodiments.

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

[0073] (2) A gypsum board comprising a set gypsum core disposed between two cover sheets, the core being formed from a slurry including stucco, water, and at least one uncooked corn starch, the at least one uncooked corn 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 at 75 rpm and 700 cmg, where the starch is placed in a slurry including water at 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) The gypsum board of embodiment 2, wherein the uncooked starch has a bulk density of about 41 pcf to about 45 pcf.

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

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

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

[0078] (7) The gypsum board of any one of embodiments 2 to 6, wherein the uncooked starch is acid-modified.

[0079] (8) The gypsum board of any one of embodiments 2-7, wherein the uncooked starch has a cold water viscosity of less than about 50 centipoise as measured according to the Brookfield Viscometer Method.

[0080] (9) The gypsum board of embodiment 8, wherein the uncooked starch has a cold water viscosity of from about 1 centipoise to about 40 centipoise.

[0081] (10) The gypsum board of embodiment 8, wherein the uncooked starch has a cold water viscosity of from about 1 centipoise to about 20 centipoise.

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

[0083] (12) The gypsum board of embodiment 11, wherein the dispersant is a naphthalene sulfonate.

[0084] (13) The gypsum board of embodiment 11 or 12, wherein the dispersant is present in an amount of about 0.1 to about 4 weight percent of the stucco.

[0085] (14) The gypsum board of 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) The gypsum board of embodiment 14 or 15, wherein the polyphosphate is present in an amount of about 0.1 to about 0.3 weight percent of the stucco.

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

[0089] (18) The gypsum board of embodiment 17, wherein the board has a density of about 20 pcf to about 31 pcf.

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

[0091] (20) A gypsum board comprising: a set gypsum core disposed between two cover sheets, the core being formed from a slurry including stucco, water, and at least one uncooked starch, the at least one uncooked starch having a cold water viscosity of about 5 centipoise to about 50 centipoise at 10% solids when the viscosity is measured at 25° C. by the Brookfield Viscometer Method.

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

[0093] (22) The 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) The gypsum board of embodiment 22, wherein the uncooked starch has a viscosity of about 300 BU to about 875 BU.

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

[0096] (25) The gypsum board of any one of embodiments 20-24, wherein the uncooked starch is acid-modified.

[0097] (26) The gypsum board of any one of embodiments 20-25, wherein the uncooked starch has a cold water viscosity of less than about 50 centipoise as measured according to the Brookfield Viscometer Method.

[0098] (27) The gypsum board of embodiment 26, wherein the uncooked starch has a cold water viscosity of from about 1 centipoise to about 40 centipoise.

[0099] (28) The gypsum board of embodiment 27, wherein the uncooked starch has a cold water viscosity of from about 1 centipoise to about 20 centipoise.

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

[0101] (30) The gypsum board of embodiment 29, wherein the dispersant is a naphthalene sulfonate.

[0102] (31) The 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) The gypsum board of 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) The gypsum board of embodiment 32 or 33, wherein the polyphosphate is present in an amount of about 0.1% to about 0.3% by weight of the stucco.

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

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

[0108] (37) The gypsum board of any one of embodiments 20-36, wherein the board has a nail pull resistance of at least about 72 lb-f according to 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 by using a Viscograph E instrument set at 75 rpm and 700 cmg, placing the starch in a slurry with water at 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.

[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 centipoise to about 50 centipoise when the viscosity is measured at 25° C. by the Brookfield Viscometer Method.

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

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

[0113] (42) The slurry of embodiment 41, wherein the uncooked starch has a viscosity of from about 300 BU to about 875 BU.

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

[0115] (44) The slurry of any one of embodiments 38-43, wherein the uncooked starch is acid-modified.

[0116] (45) The slurry of embodiment 38, wherein the uncooked starch has a cold water viscosity of less than about 50 centipoise, as measured according to the Brookfield Viscometer Method.

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

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

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

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

[0121] (50) The 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) The slurry of any one of embodiments 38-50, wherein the slurry further comprises a polyphosphate.

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

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

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

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

[0127] (56) An article made from the slurry of any one of embodiments 38-55.

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

[0129] (58) An acoustical panel comprising an acoustical component including fiber 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 by placing the starch in a slurry including water at 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 at 75 rpm and 700 cmg, and the panel having a noise reduction factor of at least about 0.5 according to ASTM C 423-02.

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

[0131] (60) A gypsum board comprising: a set gypsum core disposed between two cover sheets, the core being formed from a slurry including stucco, water, and at least one uncooked corn starch, the at least one uncooked corn starch having a hot water viscosity of about 20 Brabender units to about 300 Brabender units, as measured by the HWVA method.

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

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

[0134] (63) The gypsum board of any one of embodiments 60-62, wherein the 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 at 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 at 75 rpm and 700 cmg.

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

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

[0137] (66) The gypsum board of any one of embodiments 60-65, wherein the uncooked starch is acid-modified.

[0138] (67) The gypsum board of any one of embodiments 60-66, wherein the uncooked starch has a cold water viscosity of less than about 50 centipoise at 10% solids as measured according to the Brookfield Viscometer Method.

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

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

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

[0142] (71) The gypsum board of embodiment 70, wherein the dispersant is a naphthalene sulfonate.

[0143] (72) The gypsum board of embodiment 70 or 71, wherein the dispersant is present in an amount of about 0.1 to about 4 weight percent of the stucco.

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

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

[0146] (75) The gypsum board of embodiment 74, wherein the polyphosphate is sodium trimetaphosphate.

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

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

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

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

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

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

[0153] (82) The gypsum board of any one of embodiments 60-81, 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 about 50 centipoise at 10% solids as measured according to the Brookfield Viscometer Method, and the board has a density of about 16 pcf to about 35 pcf.

[0154] (83) The gypsum board of any one of embodiments 60-82, wherein the uncooked starch has a cold water viscosity of about 5 centipoise to about 50 centipoise at 10% solids when the viscosity is measured at 25° C. by the Brookfield Viscometer method, and 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 at 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 at 75 rpm and 700 cmg.

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

[0156] (85) A slurry comprising stucco, water, 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, as measured by the HWVA Method.

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

[0158] (87) The slurry of embodiment 85 or 86, wherein the 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 at 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 at 75 rpm and 700 cmg.

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

[0160] (89) The slurry of any one of embodiments 85-88, wherein the uncooked starch is acid-modified.

[0161] (90) The slurry of embodiment 85, wherein the uncooked starch has a cold water viscosity of less than about 50 centipoise, as measured according to the Brookfield Viscometer Method.

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

[0163] (92) The slurry of embodiment 91, wherein the uncooked starch has a cold water viscosity of from about 1 centipoise to about 20 centipoise.

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

[0165] (94) The slurry of embodiment 93, wherein the dispersant is a naphthalenesulfonate.

[0166] (95) The 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) The slurry of any one of embodiments 85-95, wherein the slurry further comprises a polyphosphate.

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

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

[0170] (99) The slurry of any one of embodiments 85-98, having a water-to-stucco ratio of about 0.4 to about 1.2.

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

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

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

[0174] (103) The slurry of any one of embodiments 85-102, wherein the 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 at 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 at 75 rpm and 700 cmg.

[0175] (104) An article made from the slurry of any one of embodiments 85 to 103.

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

[0177] (106) The method of embodiment 105, wherein the uncooked starch has a cold water viscosity of less than about 50 centipoise at 10% solids, as 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 acoustical panel comprising an acoustical component including 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 viscosity is measured by the HWVA Method, and wherein the panel has a noise reduction factor of at least about 0.5 according to ASTM C 423-02.

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

[0181] It should be noted that the foregoing are merely example embodiments. Other exemplary embodiments will be apparent from the entire description of this specification. Those skilled in the art will also understand that each of these embodiments may be used in various combinations with the other embodiments provided herein.

[0182] The following examples further illustrate the invention but, of course, should not be construed as in any way limiting its scope. EXAMPLES

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

[0186] [Table 2]

[0187] The viscosity of uncooked acid modified corn starches A-C is measured by placing the starch in a slurry containing water at a starch concentration of 15% solids, using a Viscograph E instrument set at 75 rpm and 700 cmg, where 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 maximum viscosity was recorded as the peak viscosity. Figure 1 is a Brabender amylogram of a 15% starch in water slurry, illustrating the viscosity of uncooked acid modified corn starches A-C as outlined in Table 2. In Figure 1, the X-axis is time and the Y-axis is overlaid with 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 unfoamed gypsum disc samples. The retarder was in the form of a 1% solution of the pentasodium salt of diethylenetriaminepentaacetic acid (Versenex™ 80, available from DOW Chemical Company, Midland, MI). The dispersant was in the form of a polynaphthalene sulfonate (DILOFLO, available from GEO Specialty Chemicals, Amber, PA). The disc samples were wrapped in aluminum foil and heated at 350° F. for 22 minutes and then dried at 110° F. overnight.

[0189] [Table 3]

[0190] Table 4 shows the compressive strength of non-foamed gypsum samples containing uncooked acid-modified corn starches 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 (0.5% soap solution with 1:1 ratio of unstable to stable soap) was added to a final density of 30 pcf. The retarder was in the form of a 1% solution of the pentasodium salt of 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 and heated at 350°F for 22 minutes and then dried at 110°F overnight.

[0193] [Table 5]

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

[0195] [Table 6]

[0196] As can be seen in Tables 4 and 6, the strength provided by the uncooked starch was greater than that of the pregelatinized starch. EXAMPLES

[0197] This example illustrates the wet strength of a non-foaming set gypsum composition formed from a slurry containing uncooked starch compared to two other set gypsum compositions formed from slurries containing pregelatinized starch. Wet strength was measured before the composition was placed in a kiln for drying. The wet strength of the gypsum board affects, for example, how well the wet gypsum board can be cut and how well the wet gypsum board can be turned over and transported from the knife to the kiln of a wallboard production line.

[0198] Specifically, wet strength was measured by compressive strength testing. Formulations for preparing the set 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 where the starch was formed from pregelatinized corn starch A and B, respectively, as listed in Tables 1 and 2.

[0199] [Table 7]

[0200] The dry ingredients were mixed and added to the liquid ingredients. The mixture was allowed to soak for 10 seconds and mixed with a Waring blender (Model CB15N) for 10 seconds. The slurry was poured into a 4 inch diameter, 5 / 8 inch thick ring. The wet compressive strength of the set non-foamed gypsum discs was measured 3, 5, 7, and 10 minutes after the dry ingredients were mixed with the liquid ingredients. The results are shown in Figure 2.

[0201] Surprisingly, as can be seen in FIG. 2, the samples containing uncooked, acid-modified corn starch B (Clinton 260) had stronger wet strength than the samples containing pregelatinized corn starches A and B at all time intervals. EXAMPLES

[0202] This example demonstrates the drying rate of wet boards made from slurries containing uncooked starch compared to boards made from slurries containing pregelatinized corn starch. In this regard, drying rate can affect board manufacturing processes including parameters such as energy usage, line speed, paper core bond, end burn, kiln plugging, etc.

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

[0204] [Table 8]

[0205] "PNS" refers to polynaphthalene sulfonate (DILOFLO). The retarder was in the form of a 1% solution of the pentasodium salt of diethylenetriaminepentaacetic acid (Versenex™ 80). "Gauge" water refers to the water mixed with the dry ingredients. The dry ingredients (stucco, heat accelerator, starch) were mixed and added to the liquid ingredients (10% solution of sodium trimetaphosphate, dispersant, 1% retarder solution, and water). The mixture was allowed to soak for 10 seconds and mixed for 25 seconds at speed 2 in a Hobart mixer (Model N50). Foam was generated by mixing 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 / hr. A dry core density of 31 pcf was reached after 15 seconds of foaming. The foamed slurry was poured between the front cover (Manila) and backing (Newsline) paper. The board thickness was 0.5 inches. The set boards were dried at 450° F. for 17 minutes. The weight of the boards over time is reported in FIG. 3.

[0206] As can be seen in Figure 3, the uncooked starch (acid modified corn starch B, i.e., Clinton 260) had a similar drying rate as pregelatinized corn starch B, even though heat was used 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 the hot water viscosity assay (HWVA) of starches. 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 at 15% solids in water slurry.

[0208] The test is conducted using the following procedure: Starch (60 g) in water (340 g) is formed into a slurry and transferred to a Brabender amylograph measuring bowl. The slurry is heated from 25°C to 92°C and held at 92°C for 10 minutes. The slurry is then cooled to 55°C and held at 55°C for 10 minutes. The hot water viscosity is determined upon completion of the 10 minute 92°C period.

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

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

[0211] Figure 4 demonstrates how the viscosity changes as the starch is cooked and eventually gelatinized. Torque is a measurement of viscosity since it measures the force that turns the rotor. Torque is in Brabender units. The torque at the end of the 92°C hold is defined as the hot water viscosity. This hot water viscosity represents the average molecular weight of the starch.

[0212] As can be seen from the amylogram in Figure 4, at low temperatures, before gelatinization, the viscosity does not change significantly. As the granules heat up, they will absorb water and swell. Starting at the peak of the torque curve, the granules heat up and expand enough that the granular structure breaks down and begins to separate into separate molecules. As the granular structure is broken down, the viscosity decreases until the starch is fully gelatinized, as shown in the valley of the curve. This hot water viscosity represents the average molecular weight of the starch. As the curve levels out at the valley, the solution is cooled. As a result, retrogradation occurs as the gelatinized molecules begin to associate again and the viscosity begins to increase again. EXAMPLES

[0213] This example demonstrates the hot water viscosity of certain starches compared to cooked (pregelatinized) 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 samples. The raw materials were as described in Example 3. Foam was added to a final density of 30 pcf. The foam formulation was a 0.5% soap solution with a 1:1 ratio of unstable soap:stable soap. The slurry was poured into a 1 foot by 1 foot paper envelope and heated at 450°F for 10 minutes, 375°F for an additional 15 minutes, and then dried 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 as a comparison.

[0217] Table 10 shows the hot water viscosities of the aforementioned starches as well as the nail pull strength of foamed gypsum samples formed from slurries containing uncooked acid-modified corn starch compared to foamed samples formed from slurries containing pregelatinized starch.

[0218] [Table 10]

[0219] An experimental acid-modified corn starch was modified with sulfuric acid to reach a hot water viscosity of 284. Corn starches with hot water viscosities between 30 BU and 284 BU had nail pull strengths equal to or greater than those of pregelatinized starches. However, starches with hot water viscosities of 477 BU had a negative effect on nail pull strength. Without wishing to be bound by any particular theory, it is believed that the starch molecules of uncooked acid-modified corn starch E are too large to leave the starch granules, but rather penetrate the gypsum crystal medium to increase strength. Thus, uncooked starches with hot water viscosities below 477 BU (e.g., below about 400 BU) are preferred. EXAMPLES

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

[0221] Medium hot water viscosity starch 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 starches were 0.5 N, 0.6 N, and 1.0 N, respectively. Boards 6A-6D were formed from slurries with 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 starches. Table 11 shows the hot water viscosity and nail pull strength of boards formed from acid modified tapioca, wheat and potato starches with medium hot water viscosity.

[0223] [Table 11]

[0224] Boards containing cores formed from stucco slurries containing acid-modified tapioca, wheat, and potato starches with medium hot water viscosity had similar nail pull strengths as boards containing board cores formed from slurries containing acid-modified corn starch with medium hot water viscosity. EXAMPLES

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

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

[0227] [Table 12]

[0228] As can be seen in Table 12, production boards formed from slurries containing uncooked starch exhibited similar nail pull resistance results as boards formed from stucco slurries containing pregelatinized starch. The slurries containing uncooked starch required significantly reduced water usage. EXAMPLES

[0229] This example demonstrates the use of starch in boards including board cores and thickening layers as described in U.S. Patent Application 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 thickening layer. The formulations of the slurries used in forming the core and thickening layers, respectively, of the boards are found in Tables 13A and 13B, where the other ingredients in the slurries remain relatively similar except for the heat accelerator and alum to control hydration, as described in Example 9. The starch in the board core was pregelatinized corn starch B. The starches in the thickening layers are listed in Table 14.

[0230] [Table 13A]

[0231] [Table 13B]

[0232] The boards were tested for moisture content in the gypsum slurry and nail pull resistance of the resulting boards as described herein. [Table 14]

[0233] As can be seen in Table 14, the boards had comparable nail pull results, and the thickened layer stucco slurry exhibited less water demand. EXAMPLES

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

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

[0236] [Table 15]

[0237] Two different boards, 9A and 9B, were prepared according to the formula in Table 16 using the ingredients listed in Table 16 and Example 3. Table 16 shows an unsuccessful attempt to produce a product, as shown in FIG. 6, which resulted in blistering and loss of bond before being kiln loaded. As seen in FIG. 6, board 100 is shown with the paper cover sheet 110 peeled away. Board 100 includes a core 120. Board 100 includes undesirable blistering 130, believed to be caused by poor setting properties. Table 16 also shows a similar formula with a modified amount of accelerator, which allowed to correct the defect by modifying the setting properties of the stucco slurry (i.e., by reducing the amount of accelerator) and prevent an excessively fast hydration rate.

[0238] [Table 16]

[0239] In the context of describing the present invention (particularly in the context of the claims that follow), the use of the terms "a," "an," "the," and "at least one," and similar referents, shall be construed to encompass both the singular and the plural, unless otherwise stated herein or the context clearly contradicts. The use of the term "at least one" followed by a list of one or more items (e.g., "at least one of A and B") shall be construed to mean one item selected from the listed items (A or B), or any combination of two or more of the listed items (A and B), unless otherwise stated herein or the context clearly contradicts. The terms "comprising," "having," "including," and "containing" shall be construed as open-ended terms (i.e., meaning "including but not limited to"), unless otherwise indicated. The recitation of ranges of values ​​herein is merely intended to serve as a shorthand method of individually referring to each individual value within the range, unless otherwise indicated herein, and each individual value is incorporated herein as if it were individually recited herein. All methods described herein may be performed in any suitable order, unless otherwise indicated herein or clearly contradicted by context. The term "exemplary" used herein provides an example, and does not imply the best or optimality of the recited items. The use of any and all examples or exemplary terms (e.g., "etc.") provided herein is merely intended to facilitate easier understanding of the invention, and does not impose limitations on the scope of the invention, unless otherwise stated in the claims. No term in this specification should be construed as indicating any non-claimed element as essential to the practice of the invention.

[0240] Preferred embodiments of the present invention are described herein, including the best mode known to the inventors for carrying out the invention. Variations of these preferred embodiments may become apparent to those skilled in the art upon reading the above description. The inventors expect that those skilled in the art will employ such variations as necessary, and the inventors intend for the invention to be carried out otherwise than as specifically described herein. Accordingly, the present invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the present invention unless otherwise indicated herein or clearly contradicted by context.

[0241] [Appendix 1] A gypsum board, 1. A gypsum board comprising: a set gypsum core disposed between two cover sheets, the core being formed from a slurry including 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, as measured by the HWVA method.

[0242] [Appendix 2] A gypsum board, 1. A gypsum board comprising: a set gypsum core disposed between two cover sheets, the core being formed from a slurry including 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 at 75 rpm and 700 cmg, the viscosity being measured by placing the starch in a slurry including water at a starch concentration of 15% solids, the starch being heated from 25° C. to 95° C. at a rate of 3° C. / min, the slurry being held at 95° C. for 10 minutes, and the starch being cooled to 50° C. at a rate of −3° C. / min.

[0243] [Appendix 3] A gypsum board, 1. A gypsum board comprising: a set gypsum core disposed between two cover sheets, the core being formed from a slurry including stucco, water, and at least one uncooked starch, the at least one uncooked starch having a cold water viscosity of about 5 centipoise to about 50 centipoise at 10% solids when viscosity is measured at 25° C. by the Brookfield Viscometer Method.

[0244] [Appendix 4] 3. The gypsum board of claim 1 or 2, wherein the uncooked starch has a cold water viscosity of less than about 50 centipoise at 10% solids when measured according to the Brookfield Viscometer Method at 25° C.

[0245] [Appendix 5] 5. The gypsum board of claim 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 by using a Viscograph E instrument set at 75 rpm and 700 cmg, placing the starch in a slurry containing water at 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.

[0246] [Appendix 6] The gypsum board according to any one of claims 1 to 5, wherein the slurry further comprises a foaming agent, a dispersing agent, and a polyphosphate.

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

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

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

[0250] [Appendix 10] 1. A method for preparing a gypsum board comprising: (a) mixing a slurry comprising stucco, water, and at least one uncooked starch, the at least one uncooked starch having (i) a hot water viscosity of about 20 Brabender units to about 300 Brabender units according to the HWVA method, and / or (ii) a peak viscosity of about 120 Brabender units to about 1000 Brabender units when the starch is placed in a slurry comprising water at 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 viscosity being measured by using a Viscograph E instrument set at 75 rpm and 700 cmg; (b) disposing the slurry between a first cover sheet and a second cover sheet to form a wet assembly; (c) cutting the wet assembly into boards; (d) drying the board, wherein the dried board has a hardness of about 35 pcf (560 kg / m 3 ) or less, and wherein the board has a nail pull resistance of at least about 72 lbs-f according to Method B of ASTM 473-10.

Claims

1. A gypsum board, a set gypsum core disposed between two cover sheets, the core being formed from a slurry including stucco, water, and at least one uncooked starch, the uncooked starch having a hot water viscosity of about 20 Brabender units to about 300 Brabender units when the viscosity is measured by a Hot Water Viscosity Assay (HWVA) method; The gypsum board has a density of 35 pcf or less; the gypsum board has a nail pull resistance of at least about 72 lb-f, as determined in accordance with ASTM 473-10, Method B; the uncooked starch is present in the slurry at greater than 30% by weight as a percentage of the total starch content in the slurry; Plasterboard.

2. The gypsum board of claim 1, wherein the uncooked starch has a peak viscosity of about 120 Brabender units to about 800 Brabender units when the viscosity is measured using a Viscograph E instrument set at 75 rpm and 700 cm2 by placing the uncooked starch in a slurry containing water at a starch concentration of 15% solids, heating the uncooked 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 uncooked starch to 50°C at a rate of -3°C / min.

3. The gypsum board of claim 1 or 2, wherein the uncooked starch has a bulk density of about 35 pcf to about 45 pcf, the uncooked starch is acid-modified, and the gypsum board has a density of about 16 pcf to about 35 pcf.

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

5. A gypsum board described in any one of claims 1 to 4, wherein the uncooked starch comprises acid-modified starch.

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

7. A gypsum board described in any one of claims 1 to 6, wherein the uncooked starch further comprises pregelatinized starch.

8. A gypsum board described in any one of claims 1 to 6, wherein the uncooked starch does not contain pregelatinized starch.

9. A gypsum board described in any one of claims 1 to 8, wherein the uncooked starch further comprises a mobile starch.

10. A gypsum board as described in any one of claims 1 to 9, wherein the cover sheet has a basis weight of about 33 lbs / MSF to about 45 lbs / MSF.

11. A gypsum board as described in 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 about 1,100 psi when tested according to a 2-inch cube test.

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

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

14. The gypsum board of claim 1, wherein the uncooked starch is present in the slurry at about 5% or less by weight of the stucco.

15. The gypsum board of claim 1, wherein the uncooked starch has a molecular weight of at least about 15,000 daltons.

16. A gypsum board described in any one of claims 1 to 15, wherein the uncooked starch is a non-migratory starch.

17. A method for preparing a gypsum board, comprising: (a) mixing a slurry comprising stucco, water, and at least one uncooked starch, the uncooked starch having a hot water viscosity of about 20 Brabender units to about 300 Brabender units according to the Hot Water Viscosity Assay (HWVA) method; (b) disposing the slurry between a first cover sheet and a second cover sheet to form a wet assembly; (c) cutting the wet assembly into boards; (d) drying the board, wherein the dried board has a density of about 35 pcf (560 kg / m 3 ) or less, and wherein the board has a nail pull resistance of at least about 72 lbs-f according to ASTM 473-10, Method B; (e) the uncooked starch is present in the slurry at greater than 30% by weight as a percentage of the total starch content in the slurry; method.

18. The method of claim 17, wherein the uncooked starch has a peak viscosity of about 120 Brabender units to about 800 Brabender units when the viscosity is measured using a Viscograph E instrument set at 75 rpm and 700 cmg by placing the uncooked starch in a slurry containing water at a starch concentration of 15% solids, heating the uncooked 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 uncooked starch to 50°C at a rate of -3°C / min.

19. The method of claim 17 or 18, wherein the uncooked starch has a bulk density of about 35 pcf to about 45 pcf, the uncooked starch is acid-modified, and the gypsum board has a density of about 16 pcf to about 35 pcf.

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

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

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

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

25. The method of any one of claims 17 to 24, wherein the uncooked starch further comprises a mobile starch.

26. The method of claim 17, wherein the cover sheet has a basis weight of about 33 lbs / MSF to about 45 lbs / MSF.

27. ​​The method of 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 about 1,100 psi when tested according to a 2-inch cube test.

28. The method of claim 17, wherein the uncooked starch is present in the slurry at greater than 60% by weight as a percentage of the total starch content in the slurry.

29. The method of claim 17, wherein the uncooked starch is present in the slurry at greater than 90% by weight as a percentage of the total starch content in the slurry.

30. The method of any one of claims 17 to 29, wherein the uncooked starch is present in the slurry at about 5% or less by weight of the stucco.

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

32. The method of any one of claims 17 to 31, wherein the uncooked starch is a non-migratory starch.

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