WO2019199772A1 - Gypsum panel and method for making the panel - Google Patents

Abstract

Methods of making gypsum panels are provided, including combining gypsum stucco, a starch, a glyoxal crosslinking agent, and water to form a gypsum slurry, and setting the gypsum slurry to form at least a portion of a gypsum core. Gypsum panels prepared from such methods are also provided. For example, gypsum panels may include a gypsum core that comprises set gypsum, a starch, a glyoxal crosslinking agent. Additionally, building sheathing, interior wall, or ceiling systems are provided, including at least two such gypsum panels.

Description

GYPSUM PANEL AND METHOD FOR MAKING THE PANEL

CROSS-REFERENCE TO RELATED APPLICATIONS

[1] This application claims priority benefit of ET.S. Provisional Patent Application No.

62/654,603, filed April 9, 2018, the disclosure of which is incorporated by reference herein in its entirety.

BACKGROUND

[2] The present disclosure generally relates to gypsum panels and methods of manufacturing gypsum panels, and particularly relates to gypsum panels containing crosslinking agents.

[3] Panels having a core of set gypsum have long been used as structural elements in the fabrication of buildings. Such panels, also commonly known as“wallboard,”“drywall,” or “plasterboard,” are typically used to form the partitions or walls of rooms, elevator shafts, stairwells, ceilings and the like and represent a less costly and more expeditious alternative to conventional plaster walls.

[4] In its most common form, gypsum wallboard is produced by sandwiching a solid gypsum core made from an aqueous slurry of calcined gypsum, usually a slurry of calcium sulfate hemihydrate, between two sheets of a facing material, typically heavy papers or fibrous mats, such as fiberglass. Gypsum wallboard is manufactured continuously at a high speed by continuously depositing the aqueous slurry of calcined gypsum and other ingredients onto one of the two facing sheets and then bringing the second facing sheet into contact with the free surface of the gypsum slurry to form a sandwich-like structure. [5] The calcined gypsum slurry deposited between the two facing sheets sets (i.e., the calcined gypsum reacts with water from the aqueous slurry) to form a rigid board-like structure. The so-formed board then is cut into panels of a desired length (for example, eight to sixteen feet). If the so-formed board contains excess water (water is necessary not only for hydrating the calcined gypsum but also to ensure sufficient fluidity of the gypsum slurry during preparation of the board), the board may then pass through a drying kiln in which excess water is removed and the gypsum wallboard is brought to a final hydrated, but dry state. After the core has been set and is fully dried, the sandwich becomes a rigid, fire-resistant building material.

[6] However, it would be desirable to produce gypsum panels having improved strength and/or an improved bond between the gypsum core and the panel facer material.

SUMMARY

[7] In one aspect, methods of making gypsum panels are provided, including combining gypsum stucco, a starch, a glyoxal crosslinking agent, and water to form a gypsum slurry; and setting the gypsum slurry to form at least a portion of a gypsum core.

[8] In another aspect, gypsum panels prepared from such methods are provided. For example, gypsum panels may include a gypsum core that comprises set gypsum, a starch, a glyoxal crosslinking agent.

[9] In yet another aspect, building sheathing, interior wall, or ceiling systems are provided, including at least two such gypsum panels. BRIEF DESCRIPTION OF THE DRAWINGS

[10] Referring now to the drawings, which are meant to be exemplary and not limiting, and wherein like elements are numbered alike. The detailed description is set forth with reference to the accompanying drawings illustrating examples of the disclosure, in which use of the same reference numerals indicates similar or identical items. Certain embodiments of the present disclosure may include elements, components, and/or configurations other than those illustrated in the drawings, and some of the elements, components, and/or configurations illustrated in the drawings may not be present in certain embodiments.

[11] FIG. 1 is a cross-sectional view of a gypsum panel having a paper material facer.

[12] FIG. 2 is a cross-sectional view of a gypsum panel having two paper material facers.

[13] FIG. 3 is a schematic depiction of a process of producing a gypsum wallboard.

[14] FIG. 4 is a perspective view of a building sheathing system.

[15] FIG. 5 is a bar graph showing the results of the nail pull test of the Examples.

[16] FIG. 6 is a bar graph showing the results of the compressive strength test of the

Examples.

[17] FIG. 7 is a bar graph showing the results of the humid bond test of the Examples.

DETAILED DESCRIPTION

[18] Gypsum panels and systems of panels, and methods for their manufacture, are provided herein. The panels (also referred to interchangeably herein as“boards”) display improved mechanical properties, such as nail pull and flexural strength, compressive strength, and humid bond between the gypsum core and the panel facer material. In particular, it has been discovered that utilizing a crosslinking agent containing glyoxal, in combination with starch, to form a gypsum core results in improved mechanical properties.

[19] Methods of making gypsum panels, and the resulting panels, will be described in detail.

It should be understood that although features of the disclosure may be described with reference to particular embodiments, the disclosure is meant to encompass any number of variations, alterations, substitutions, or equivalent arrangements not explicitly described herein, and should not be limited to such explicitly disclosed embodiments.

[20] Methods of Making Gypsum Panels

[21] In one aspect, methods of making gypsum panels are provided herein, including combining gypsum stucco, a starch, a glyoxal crosslinking agent, and water to form a gypsum slurry, and setting the gypsum slurry to form at least a portion of a gypsum core.

[22] The starch may be any suitable starch known in the industry. For example, the starch may or may not be pregelatinized.“Pregelatinized starch,” which is also termed cold-swelling starch, has been chemically and/or mechanically processed to rupture all or part of the starch granules. In contrast to native starch, pregelatinized starch can be soluble in cold water, or can form dispersions, pastes, or gels with cold water, depending on the concentration of the pregelatinized starch used and on the type of starch used to produce the pregelatinized starch. In principle it is possible to produce pregelatinized starch by various processes, for example by wet- thermal digestion using a roller dryer, mechanical, and thermal treatment with an extruder, or exclusively mechanical treatment with a vibratory mill. In all processes the starch grain structure and the para-crystalline molecular organization is disrupted, and the starch is converted into an amorphous substance. In addition to pregelatinization, the starches can be further physically modified, e.g., by extrusion, spray drying, drum drying, and agglomeration. [23] Starch is predominantly present in plants and seeds as amylose and amylopectin.

Depending on the plant, starch generally contains 20 to 25 percent amylose and 75 to 80 percent amylopectin. Polysaccharide starches include maize or com, waxy maize, potato, cassava, tapioca and wheat starch. Other starches include varieties of rice, waxy rice, pea, sago, oat, barley, rye, amaranth, sweet potato, and hybrid starches available from conventional plant breeding, e.g., hybrid high amylose starches having amylose content of 40% or more, such as high amylose corn starch. Also useful are genetically engineered starches such as high amylose potato and waxy potato starches.

[24] In certain embodiments, the starches can be chemically modified or derivatized, such as by etherification, esterification, acid hydrolysis, dextrinization, crosslinking, cationization, heat- treatment or enzyme treatment (e.g., with alpha-amylase, beta-amylase, pullulanase, isoamylase, or glucoamylase). One exemplary starch is a hydroxyalkylated starch such as a

hydroxypropylated or hydroxy ethylated starch, and succinated starches such as

octenylsuccinated or dodecyl succinated starches. Low amylose starches can also be used. As used herein, the term“low amylose” is intended to include starches containing less than 40% by weight amylose. One commercially available starch is hydroxypropylated starch available from National Starch and Chemical Company. Other commercially available types of starches are waxy starches, also available from National Starch and Chemical Company. As used herein, the term“waxy” is intended to include a starch containing at least 95% by weight amylopectin.

[25] In some embodiments, the pregelatinized starch is a non-gelling starch, i.e., any native or modified starch having a modulus of less than 100 Pa at 10-1 rad/s, at 25° C., and at 5% solids dissolved in water. Exemplary non-gelling starches include those that are stabilized, including hydroxyalkylated starches such as hydroxypropylated or hydroxyethylated starches, and acetylated starches. In another embodiment, non-gelling starches include dextrinized starches.

In a further embodiment, non-gelling starches include modified waxy and modified high amylose starches. Non-limiting examples of highly converted starches are highly converted sago, highly converted tapioca, and highly converted corn starch. Converted starch is starch that has been changed to a lower molecular form through various modifications. Modifications to convert starch to lower molecular weight are well known in the art. In one embodiment, non-gelling starches have a low viscosity, with a water fluidity in the range of from 40 to 90. In another embodiment, the starches will have a water fluidity in the range of 65 to 85. Water fluidity is known in the art and, as used herein, is measured using a Thomas Rotational Shear-type

Viscometer (commercially available from Arthur A. Thomas Co., Philadelphia, Pa.),

standardized at 30° C with a standard oil having a viscosity of 24.73 cps, which oil requires 23.l2±0.05 sec for 100 revolutions. Accurate and reproducible measurements of water fluidity are obtained by determining the time which elapses for 100 revolutions at different solids levels depending on the starch's degree of conversion: as conversion increases, the viscosity decreases. The conversion may be by any method known in the art including oxidation, enzyme conversion, acid hydrolysis, heat, and/or acid dextrinization.

[26] Thus, in one embodiment the pregelatinized starch is a pregelatinized starch that has been chemically modified with a mono-reactive moiety to a degree of substitution of at least 0.015. In a particular embodiment, the pregelatinized starch is selected from the group consisting of ether and ester derivatives of starch, such as hydroxypropyl, hydroxyethyl, succinate, and octenyl succinate starch. In one specific embodiment the starch is a hydroxypropylated potato starch having a degree of substitution of 0.015-0.30 and a molecular weight of 200,000-2,000,000. Another specific embodiment comprises hydroxy ethylated dent corn starch having a degree of substitution of 0.015-0.3 and a molecular weight of 200,000-2,000,000. Another specific embodiment comprises hydroxypropylated high-amylose com starch with a degree of substitution of 0.015-0.3 and a molecular weight of 200,000-2,000,000.

[27] A variety of different types of pregelatinized starch are commercially available and can be used. An exemplary pregelatinized starch material is cold-water-soluble granular

pregelatinized starch materials produced, for example, as described in U.S. Pat. No. 4,465,702 to Eastman et al. A pregelatinized com starch of this type is available under the trade name MIRAGEL® 463, manufactured by the A. E. Staley Manufacturing Company, which thickens and sets to a gel using room temperature water. Other pregelatinized starches that can be used include ETltra Sperse® M, from National Starch and Chemical Company of Bridgewater, N.J.; pregelatinized waxy corn starch, available from National Starch and Chemical Company; and a pregelatinized, hydroxy ethylated dent corn starch available under the trade name Staramic® 747, from A. E. Staley Mfg. Co. of Decatur, Ill.; and the hydroxy ethylated dent com starches available under the trade names ETHYLEX® 2005-2095 from Tate & Lyle, ETC.

[28] The relative amounts of the starch and the stucco will vary, depending on the desired properties of the gypsum board, the type of starch and gypsum used, and the presence and amounts of other optional additives. For example, the starch may be present in the slurry from which the gypsum core (or a portion thereof) is formed in an amount of up to about 3 weight percent (wt. %), based on the gypsum stucco weight. For example, the starch may be present in the slurry in an amount of from about 0.2 wt. % to about 2 wt. %, or from about 0.3 wt. % to about 1 wt. %, based on the gypsum stucco weight. In certain embodiments, the starch is present in the slurry in an amount of up to 20 pounds per 1,000 square feet (msf), such as from about 5 to about 15 pounds/msf. [29] It has been discovered that in gypsum panels containing starch, a glyoxal based crosslinking agent may be used to effectively crosslink the starch and thereby improve the mechanical properties of the resultant core and board, such as nail pull and flexural strength, compressive strength, and humid bond between the gypsum core and the panel facer material.

The glyoxal crosslinking agent may be any suitable glyoxal based agent that is effective to crosslink starch.

[30] In certain embodiments, the glyoxal crosslinking agent is a dialdehyde, such as Berset® 2040, commercially available from Bercen, Inc. In certain embodiments, the glyloxal crosslinking agent is a modified glyoxal, such as Berset® 2125, commercially available from Bercen, Inc. In certain embodiments, the glyoxal crosslinking agent is a blocked glyoxal crosslinking agent, such as Berset® 2269, commercially available from Bercen, Inc.

[31] The glyoxal crosslinking agent may be provided in any suitable amount, which is typically based on the relative amount of starch present in the slurry. For example, the glyoxal crosslinking agent may present in the slurry in an amount of from about 1 to about 100 percent, by weight, relative to the weight of the starch. In some embodiments, the glyoxal crosslinking agent is present in the slurry in an amount of from about 1 to about 50 percent, by weight, relative to the weight of the starch, such as from about 5 to about 30 percent, by weight, relative to the weight of the starch, or from about 10 to about 30 percent, by weight, relative to the weight of the starch. In certain embodiments the glyoxal crosslinking agent is combined with the other ingredients of the gypsum slurry in a liquid form.

[32] In certain embodiments, a dispersant is also added to the gypsum slurry. For example, because the presence of starch increases the amount of water needed to hydrate the slurry, a dispersant may be effective to reduce the amount of water necessary. Any suitable dispersants known in the industry may be used, such as naphthalene sulfonate based dispersants. For example, the dispersant is present in the slurry in an amount of from about 2 to about 12 pounds/msf.

[33] As in any gypsum wallboard, the largest single ingredient, other than possibly water, in the gypsum slurry is a source of calcined gypsum, usually calcium sulfate hemihydrate, commonly referred to as“stucco” or“Plaster of Paris.” Generally, a wide amount of calcined gypsum can be used in preparing the gypsum slurry. The calcined gypsum typically comprises about 30 weight percent to about 60 weight percent of the gypsum slurry, such as from about 40 to 50 weight percent of the gypsum slurry. However, this disclosure is not limited to any particular source of the calcined gypsum and can use calcined gypsum made from both natural minerals extracted from quarries, and from synthetic gypsums, known as desulfogypsum, produced from the desulfurization of electrical power plant flue gas effluents (i.e., FGD gypsum). Calcined gypsum made from a combination of natural and synthetic gypsum also can be employed. Following hydration and drying, the set gypsum typically constitutes more than 85 percent, by weight, of the set gypsum core.

[34] Whether natural rock or synthetic, the gypsum may be dried, ground, calcined, and stored as stucco, which is calcium sulfate hemihydrate. The drying step of stucco manufacture typically includes passing crude gypsum rock through a rotary kiln to remove free moisture, and then grinding the rock to a desired fineness, using for example a roller mill. The dried, ground gypsum, often referred to as“land plaster,” then is typically heated in a“calciner” to remove water of hydration and yield the calcined gypsum that exhibits the valuable property of being chemically reactive with water, and setting to form a rigid structure. There are two forms of stucco, alpha (a) calcium sulfate hemihydrate and beta (b) calcium sulfate hemihydrate. As will be appreciated by those skilled in the art, these two types of stucco are produced by different calcination procedures. The present disclosure can generally use either the beta or the alpha form of stucco; though, as is the case in conventional gypsum wallboard production, the less costly beta form is usually used.

[35] In certain embodiments, the calcined gypsum is mixed, typically in a“pin” mixer, with the starch and the glyoxal crosslinking agent and any other additives, in the presence of water, to form a gypsum slurry. Thus, the aqueous gypsum slurry contains at least gypsum, water, starch, and the glyoxal crosslinking agent; however, other additives will commonly be used. For example, any suitable additives known in the industry may be used. For example, suitable additives may include agents to reduce the density of the gypsum core (such as foaming agents, surfactants, microspheres), dispersants (as discussed above), set retarders, set accelerators, biocides (mold and mildew control agents), fillers, water resistance additives (such as a wax or a wax emulsion or siloxanes), fire retardants, reinforcing fibers (such as chopped glass fibers or other inorganic fibers), strength-enhancing agents (such as sodium trimetaphosphate or polymeric binders) and combinations thereof.

[36] An amount of water also is included in the gypsum slurry to ensure proper flowability of the slurry. Water is added to the process to hydrate the calcined gypsum, to provide needed fluidity. As is the case in conventional wallboard production, most of this water must eventually be driven off by heating the set gypsum wallboard. Thus, the lower the amount of water used, the lower the drying costs. In certain embodiments, the weight ratio of water to calcined gypsum can range over a wide range of weight ratios (i.e., weight of water divided by weight of calcined gypsum). In some embodiments, the water-to-calcined gypsum weight ratio (water: calcined gypsum) is established in the range of about 0.5: 1, to about 1.5: 1, such as from about 0.7: 1 to about 1.3: 1.

[37] The gypsum slurry may be formed into a long, continuous sheet between two layers of facing material. In an alternative embodiment, the gypsum slurry may be placed in a mold.

[38] One method for preparing a wallboard in accordance with the present disclosure is illustrated schematically in FIG. 3. In this embodiment, the calcined gypsum is fed into the top of a mixer of the type commonly referred to as a pin mixer (not shown) along with other dry components. In particular, the halide salt sequestration agent and any other optionally included dry additive components from which the gypsum slurry is formed can be pre-mixed and then fed as a dry mixture to the pin mixer. Water and other liquid constituents (e.g., soap or foam, prepared separately using high shear mixing and used to control the slurry density), used in forming the gypsum slurry, are also metered into the pin mixer through other ports where they are combined with the dry components to form an aqueous gypsum slurry 12, which emerges from a discharge conduit 11 of the pin mixer. The residence time in the pin mixer usually is very short.

[39] The slurry is deposited through one or more outlets of the discharge conduit 11 onto a continuous, horizontally moving lower facing sheet 10 comprising a facing material (e.g., paper) which may be slightly wider than the desired width of the wallboard. The lower facing sheet 10 and the deposited gypsum slurry 12 move in the direction of arrow A. An upper facing sheet 13, also including a material such as paper, is fed in the direction of arrow B from a roll (not shown) and applied to the upper surface of the gypsum slurry 12. The“sandwich” of slurry and adjacent facing sheets is then passed through a mold or other forming device (rollers, guides, or plates (14 and 15)) for establishing the desired width and thickness of the gypsum board. The amount of slurry deposited can be controlled in a manner known in the art such that it, in cooperation with plates 14 and 15 and the facing sheets 10 and 13, form a board of the desired width and thickness. Facing sheets 10 and 13 are usually of a type of paper, such as multi-ply paper, commonly used for the face sheet of wallboard products, although other facing materials may be used. Such paper products are known to those skilled in the art.

[40] The lower facing sheet 10 is fed from a roll (not shown). In some embodiments, prior to receiving the gypsum slurry 12, the lower facing sheet 10 may be scored by one or more scoring devices, allowing the edges of lower facing sheet 10 to be folded upward and around the deposited gypsum slurry. These edges may then be glued or adhered with a gypsum slurry to overlapping portions of an upper facing sheet 13 according to methods known in the art. Prior to applying the (upper) facing sheet 13 to the upper surface of the gypsum slurry, glue may be applied to the facing sheet along portions of the sheet that will overlap and be in contact with the folded-over mat edges (glue application is not shown).

[41] In certain embodiments, the gypsum core includes multiple layers that are sequentially applied to the fiberglass mat, and allowed to set either sequentially or simultaneously. In other embodiments, the gypsum core includes a single layer. Though not shown, the present disclosure also contemplates that, in certain embodiments, a minor portion of the gypsum slurry may be discharged through an appropriate outlet to provide a relatively thin layer of gypsum slurry on the inner surface of facing sheets 10 and 13. The thin layer of gypsum slurry is somewhat denser than the aqueous slurry of gypsum used to form the main portion of the set gypsum core (main core slurry discharged through outlet 11 to form gypsum slurry layer 12). This higher density region of the core (also known as the“slate coat”) is intended to assist in the formation of a strong bond between the lower density portion of the core and the facing sheets, such as by penetrating into the interstices of a fibrous facing material.

[42] In some embodiments, the slurry used to form the slate coat layer is about 18 to 20 percent denser than the density of the slurry used to form the main portion of the set gypsum core. In certain embodiments, depositing the gypsum slurry includes depositing a first gypsum slurry having a wet density of from about 88 pcf to about 98 pcf onto the surface of a fiberglass mat, the first gypsum slurry. In certain embodiments, the first gypsum slurry has a wet density of from about 93 pcf to about 96 pcf. In some embodiments, the gypsum core includes at least three gypsum layers, with the outermost gypsum layers of the gypsum core (i.e., the layers that form an interface with the facer mats) being slate coat layers. In certain embodiments, both outermost layers have a relatively high density or are otherwise chemically altered for enhanced penetration. Thus, a third gypsum slurry may have a wet density of from about 88 pcf to about 98 pcf, or from about 93 pcf to about 96 pcf. In certain embodiments, the first gypsum slurry (or each of the outermost gypsum slurry layers) is deposited in an amount of from about 5 percent to about 20 percent, by weight, of the gypsum core. In addition, it also is contemplated that, in some embodiments, some of this higher density gypsum slurry also can be used to form streams of gypsum slurry at each of the edges of the facing sheets to form hard edges of the wallboard.

[43] In the illustrated embodiment, the nascent board 16 then travels on rollers or on a conveyor 17 in the direction of arrow C for several minutes. During this time, the slurry is allowed to set and form the hardened gypsum core by hydration of the stucco. During this setting process, the core hardens as the gypsum mineral (calcium sulfate dihydrate) is formed.

[44] Wallboard panels are then cut to length, flipped, and dried, such as in a continuous oven or by allowing the material(s) to set at room temperature (i.e., to self-harden). The individual boards may then be taped face-to-face in pairs and stacked for shipment. For molded articles, the gypsum slurry is alternatively introduced directly into a mold and the slurry sets to form the article.

[45] As noted above, in certain embodiments, the slurry contains more water than necessary solely to reconstitute the gypsum from stucco. This extra water is used in the board forming stage to reduce the stucco slurry viscosity sufficiently to allow for its even distribution (e.g., by using a forming roll) across and between the facing sheets at a desired thickness. Because of the use of excess water, the gypsum board remains wet after hydration (although it is possible at this point the board can be cut to desired dimensions). Therefore, the formed board ultimately may be dried.

[46] In certain embodiments, the drying operation involves applying heat by circulating hot air (e.g., in a drying oven) around the wet gypsum board to evaporate the excess water. It may be necessary, therefore, that the facing sheets be sufficiently porous to allow this excess water to readily evaporate without adverse effects such as delamination, tearing, bursting, etc. of the facing sheets. The ability of the facing sheets to allow the escape of water vapor may also promote a uniform degree of dryness. This may improve overall board quality, since

insufficiently dried gypsum board presents storage problems, while over-drying leads to calcination and causes a loss of mechanical strength. Typical drying conditions may involve maintaining an ambient or surrounding hot air temperature from 200° F to 600° F (about 95° C to 315° C) for a drying time from 10 minutes to 2 hours. For example, at line speeds of about 70 to about 600 linear feet per minute, drying times of about 30 to about 60 minutes may be used. However, these parameters are exemplary and are influenced by the particular configuration of the board manufacturing line. [47] Conventional gypsum wallboard, at a nominal thickness of ½ inch or inch, typically is prepared at a weight between about 1,000 to about 2,100 pounds/msf of board. This corresponds to a board density of about 24 to about 48 lb/ft³. The gypsum wallboards prepared in accordance with this disclosure may have such relatively high weight and densities, or may have a reduced density relative to a standard wallboard. For example, reducing the weight of each gypsum wallboard panel by as little as 30 pounds/msf can result in significant savings. For example, by adjusting the proportion of foam in the gypsum slurry, the set gypsum core of the present disclosure may have a much lower density than commercially available gypsum products. In certain embodiments, a gypsum wallboard of the present disclosure at a nominal thickness of ½ inch has a weight between about 1,000 to about 1,500 pounds/msf of board. In certain embodiments, a gypsum wallboard of the present disclosure at a nominal thickness of 5/8 inch has a weight between about 1,000 to about 2,100 pounds/msf of board, such as about 1,500 pounds/msf to about 2,100 pounds/msf.

[48] In certain embodiments, the gypsum core includes about 80 weight percent or above of set gypsum (i.e., fully hydrated calcium sulfate). For example, the gypsum core may include about 85 weight percent set gypsum. In some embodiments, the gypsum core includes about 95 weight percent set gypsum.

[49] The facing sheets, also referred to interchangeably herein as“facer materials” or“facer mats”, may comprise any fibrous material known to be suitable for facing gypsum board.

Specific materials include paper, such as heavy, single, or multi-ply paper (e.g., medium or heavy Kraft paper, manila paper, etc.) and cardboard. For example, multi-ply paper used for the facing sheet of gypsum board products may have a basis weight from 40 to 65 pounds/msf an overall caliper of 250 to 350 microns, and a Gurley porosity from 15 seconds to 145 seconds. In some embodiments, different types of paper are used for each gypsum board surface. For example, manila paper may be used on one side, while newsliner may be used on the opposite side.

[50] Paper and cardboard facing materials may be made from recycled fibers (e.g., used corrugated paper, Kraft cuttings, or waste newsprint), but they may also be partially or wholly made from virgin fibers. Other natural or synthetic fibrous materials also can be used, including those derived from metals or glass (e.g., fiberglass mat, chopped or continuous strand mat, or glass roving, both woven and non-woven). Other useful materials for the facing sheet include filament forming synthetic organic polymers (e.g., nylon, polyesters, polypropylene, polyethylene, rayon, and cellulosics), ceramics, cotton, cloth, hair, felt, and the like. Fibrous mats can be bound with, or coated with a resin binder. Multiple layers of fibrous materials, for example a composite sheet of a glass mat and Kraft paper, may also be used.

[51] In certain embodiments, one or both of the mat facers may be coated, on the external and/or internal surfaces of the mat facer, to provide additional performance characteristics of the panel and/or facer.

[52] Gypsum Panels & Systems

[53] Gypsum panels, and systems of such panels, are also provided herein. The gypsum panels may be manufactured to have any of the properties, or via any of the methods, described herein. In certain embodiments, a gypsum panel contains a gypsum core that comprises set gypsum, a starch, a glyoxal crosslinking agent. For example, such panels may display enhanced strength and facer bonding properties. In certain embodiments, as described above, the starch may be pregelatinized starch and/or the glyoxal crosslinking agent is a blocked glyoxal crosslinking agent. [54] In certain embodiments, as shown in FIG. 1, a gypsum panel 100 includes a gypsum core 101 having a first surface and a second opposed surface, and a first facer mat 104 associated with the first surface of the gypsum core 101, such that gypsum of the gypsum core penetrates and/or adheres to at least a portion of the first facer mat 104. The various layers are illustrated as separate layers in the figures for ease of illustration; however, it should be understood that overlap of these materials may occur at their interfaces.

[55] In certain embodiments, as shown in FIG. 2, the gypsum core 101 includes two or more gypsum layers 102, 108. For example, the gypsum core may include various gypsum layers having different compositions. In some embodiments, the first gypsum layer 102 that is in contact with the facer mat 104 is a slate coat layer, as discussed above. In some embodiments, the first gypsum layer 102 is present in an amount from about 5 percent to about 20 percent, by weight, of the gypsum core 101. In certain embodiments, as shown in FIG. 2, the gypsum panel 100 includes two facer material mats 104, 112 that are associated with the gypsum core 101.

[56] As discussed above, the panels may have a thickness from about ¼ inch to about 1 inch. For example, the panels may have a thickness of from about ½ inch to about 5/8 inch. In certain embodiments, the panels have a weight of from about 1,000 to about 2,100 pounds/msf.

[57] In certain embodiments, as will be understood with reference to the Examples, the gypsum panel displays one or more enhanced mechanical properties. In certain embodiments, the gypsum panel displays a nail pull of about at least about 70 pounds force. For example, the panel may display these improved properties in the absence of sodium trimetaphosphate.

[58] Building sheathing systems are also provided herein, and include at least two of gypsum panels described herein, including any features, or combinations of features, of the panels described herein. For example, the gypsum panels may each include a gypsum core containing starch and a glyoxal crosslinking agent. In certain embodiments, as shown in FIG. 4, a building sheathing system includes at least two gypsum panels 300 and a seaming component 320 configured to provide a seam at an interface between at least two of the gypsum panels 300. In certain embodiments, the seaming component comprises tape or a bonding material.

[59] Interior building walls and/or ceiling systems are also provided herein, and include at least two of the gypsum panels described herein. For example, the gypsum panels may each include a gypsum core containing starch and a glyoxal crosslinking agent.

[60] Examples

[61] Gypsum panels formed from gypsum slurries containing starch and a glyoxal

crosslinking agent, as disclosed herein, were manufactured and tested according to the following examples.

[62] First, sample panels having cores made from slurries containing starch, a dispersant, FGD gypsum stucco, and a crosslinking agent were manufactured according to the parameters set forth in Table 1 below. A control containing no crosslinking agent was also prepared. The crosslinking agents included three glyoxal based crosslinking agents and sodium

trimetaphosphate. The sample panels were faced with paper facing materials, with the front face paper having a weight of 54 pounds/msf and the back face having a weight of 42 pounds/msf.

Table 1: Glyoxal Crosslinking Starch Gypsum Wallboard Prototype Parameters

[63] The samples were tested for various mechanical properties and the results are shown in FIGS. 5-7. First, the nail pull strength of each panel was tested. The samples containing modified glyoxal and blocked glyoxal each outperformed the control, with the sample containing blocked glyoxal surprisingly having a higher nail pull value than even the STMP sample, which is considered to have very high mechanical strength properties in the industry. Thus, without intending to be bound by a particular theory, it has been surmised that glyoxal and its derivatives can effectively crosslink starch to further enhance the strength performance of gypsum boards. Indeed, a 25% higher nail pull was observed over the control without a crosslinker. FIG. 5 is a bar graph showing the results of the nail pull test.

[64] Next, the samples were tested for their compressive strength. FIG. 6 is a bar graph showing the results of the compressive strength test. Again, the samples containing modifed and blocked glyoxal performed similarly or better than the sample containing STMP. [65] Last, the samples were tested for their humid bond strength for bonding the core to the paper facer. FIG. 7 is a bar graph showing the results of the humid bond test. Again, the samples containing blocked glyoxal were similar to or better than the control and STMP containing panel.

[66] Thus, it has been discovered that glyoxal based crosslinking agents can be employed to crosslink starch in gypsum panel cores to enhance the mechanical properties of gypsum products, such as nail pull and flexural strength, compressive strength and humid bond. The crosslinked starch displays higher tensile strength and toughness, better water resistance, good dimensional stability and processability. Such enhancement of wallboard strength performance using glyoxal crosslinking chemistry, and in particular blocked glyoxal, was observed in testing.

[67] While the disclosure has been described with reference to a number of embodiments, it will be understood by those skilled in the art that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions, or equivalent arrangements not described herein, but which are commensurate with the spirit and scope of the invention. Additionally, while various

embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.

Claims

CLAIMS What is claimed is:

1. A method of making a gypsum panel, comprising:

combining gypsum stucco, a starch, a glyoxal crosslinking agent, and water to form a gypsum slurry; and

setting the gypsum slurry to form at least a portion of a gypsum core.

2. The method of claim 1, wherein the starch comprises pregelatinized starch.

3. The method of claim 1, wherein the glyoxal crosslinking agent is a blocked glyoxal crosslinking agent.

4. The method of claim 1, wherein the glyoxal crosslinking agent is present in the slurry in an amount of from about 1 to about 100 percent, by weight, relative to the weight of the starch.

5. The method of claim 1, wherein the glyoxal crosslinking agent is present in the slurry in an amount of from about 1 to about 50 percent, by weight, relative to the weight of the starch.

6. The method of claim 1 wherein the glyoxal crosslinking agent is present in the slurry in an amount of from about 5 to about 30 percent, by weight, relative to the weight of the starch.

7. The method of claim 1, wherein the glyoxal crosslinking agent is present in the slurry in an amount of from about 10 to about 30 percent, by weight, relative to the weight of the starch.

8. The method of claim 1, wherein the starch is present in the slurry in an amount of up to 20 pounds/msf.

9. The method of claim 1, wherein the starch is present in the slurry in an amount of from about 5 to about 15 pounds/msf.

10. The method of claim 1, wherein the gypsum slurry further comprises a dispersant.

11. The method of claim 10, wherein the dispersant comprises naphthalene sulfonate.

12. The method of claim 10, wherein the dispersant is present in the slurry in an amount of from about 2 to about 12 pounds/msf.

13. The method of claim 1, wherein the glyoxal crosslinking agent is combined in a liquid form to form the gypsum slurry.

14. The method of claim 1, further comprising associating a facer material with the gypsum slurry or the gypsum core to form a gypsum panel.

15. The method of claim 14, further comprising depositing the gypsum slurry onto the facer material to form the gypsum panel.

16. The method of claim 15, wherein the facer material comprises a paper facer material.

17. The method of claim 1, wherein the gypsum panel has a weight of from about 1,000 to about 2,100 pounds/msf.

18. The method of claim 1, wherein the gypsum panel displays a nail pull of about at least about 70 pounds force.

19. A gypsum panel made from the method of any one of claims 1 to 18.

20. A gypsum panel, comprising a gypsum core that comprises set gypsum, a starch, a glyoxal crosslinking agent.

21. The gypsum panel of claim 20, wherein the starch comprises pregelatinized starch.

22. The gypsum panel of claim 20, wherein the glyoxal crosslinking agent is a blocked glyoxal crosslinking agent.

23. The gypsum panel of claim 20, wherein the glyoxal crosslinking agent is present in the core in an amount of from about 1 to about 100 percent, by weight, relative to the weight of the starch.

24. The gypsum panel of claim 20, wherein the glyoxal crosslinking agent is present in the core in an amount of from about 1 to about 50 percent, by weight, relative to the weight of the starch.

25. The gypsum panel of claim 20, wherein the glyoxal crosslinking agent is present in the core in an amount of from about 5 to about 30 percent, by weight, relative to the weight of the starch.

26. The gypsum panel of claim 20, wherein the glyoxal crosslinking agent is present in the core in an amount of from about 10 to about 30 percent, by weight, relative to the weight of the starch.

27. The gypsum panel of claim 20, wherein the starch is present in the core in an amount of up to 20 pounds/msf.

28. The gypsum panel of claim 20, wherein the starch is present in the core in an amount of from about 5 to about 15 pounds/msf.

29. The gypsum panel of claim 20, wherein the core further comprises a dispersant.

30. The gypsum panel of claim 29, wherein the dispersant comprises naphthalene sulfonate.

31. The gypsum panel of claim 29, wherein the dispersant is present in the core in an amount of from about 2 to about 12 pounds/msf.

32. The gypsum panel of claim 20, further comprising a facer material associated with the gypsum core.

33. The gypsum panel of claim 32, wherein the facer material comprises a paper facer material.

34. The gypsum panel of claim 20, wherein the gypsum panel has a weight of from about 1,000 to about 2,100 pounds/msf.

35. The gypsum panel of claim 20, wherein the gypsum panel displays a nail pull of about at least about 70 pounds force.

36. A building sheathing, interior wall, or ceiling system, comprising at least two of the gypsum panels of any one of claims 20 to 35.