Method for recycling a gypsum panel containing a hydrophobic material and uses thereof

Abstract

1. A method for making a gypsum board, the method comprising: combining a first plurality of particles comprising at least about 50% by weight calcium sulfate dihydrate and about 0.05% to about 10% by weight hydrophobic material, the first plurality of particles having a D50 particle size of about 200 μm to about 800 μm, with a second plurality of particles comprising calcium sulfate hemihydrate to form a combined calcium sulfate mixture; adding water to the combined calcium sulfate mixture to create an aqueous gypsum slurry; depositing a core layer comprising the aqueous gypsum slurry on a forming surface; and allowing the core layer to harden, thereby forming a hardened gypsum core.

Description

Technical Field

[0001] The present disclosure relates to a method for recycling gypsum board waste.

Background Art

[0002] In building construction, one of the most common building elements is gypsum board, also known as gypsum paneling, gypsum building panel, gypsum panel, or wallboard, which is used in the construction of walls and / or ceilings. Walls made of gypsum wallboard are traditionally constructed by fixing the panels to wooden studs or metal frameworks and treating the joints between adjacent panels with a specially prepared adhesive called joint compound. Gypsum panels are easily adaptable to walls of irregular sizes and can be shaped around structural elements such as beams or pipes. Since the side edges of drywall panels are tapered, it allows the application of joint compound to the seams between adjacent panels so that a monolithic surface is created during finishing.

[0003] Gypsum board is made mainly of gypsum, in contrast to cement board, which is mainly cement such as Portland cement. In particular, gypsum board is mainly composed of calcium sulfate dihydrate. Gypsum board is made by reacting water and stucco (calcium sulfate hemihydrate) so that the calcium sulfate hemihydrate hardens to form calcium sulfate dihydrate (gypsum). Stucco is made by firing gypsum, which typically consists mainly of calcium sulfate hemihydrate and may also contain calcium sulfate anhydride. Calcium sulfate hemihydrate is produced by firing calcium sulfate dihydrate to partially dehydrate the calcium sulfate dihydrate.

[0004] When stucco is mixed with water, the calcium sulfate hemihydrate particles react and rehydrate to form hardened gypsum. The method of manufacturing a gypsum panel typically involves depositing an aqueous gypsum slurry (e.g., a mixture containing stucco and water). Optionally, one or more additives can be added to the slurry. Additives can include, for example, retarders, accelerators, foaming agents, wet strength improving materials, biocides, durability components, cellulose fibers, glass fibers, flame retardant materials, binders, water repellent components, dust reducing agents, starch, and other components or improving materials known in the art. The slurry is typically deposited on a moving continuous facer sheet of paper or fiber mat, and then this slurry is covered with another facer sheet of paper or fiber mat such that the aqueous gypsum slurry forming the gypsum core is sandwiched between two opposing materials. To reduce the overall weight of the finished gypsum board, air can be incorporated into the aqueous gypsum slurry as air bubbles or air pockets, resulting in a gypsum board having a foamed or bubbled gypsum core with pores of air (also called air bubbles). The gypsum slurry is hardened (e.g., to form an interlocking matrix of calcium sulfate dihydrate, also known as hardened gypsum), cut into panels, and made into solid articles before being sent to a kiln for final drying. The resulting gypsum board is further processed as known in the art and then bundled and made ready for shipment.

[0005] There are many different types and sizes of gypsum boards to meet specific construction needs, such as gypsum exterior building panels, tile backer boards, or interior drywall. For example, moisture-resistant drywall can be manufactured for use in applications where the drywall may be exposed to water, such as in bathrooms or outdoor applications. When installing gypsum boards in the building industry, waste materials are generated.

[0006] Gypsum boards can enter the solid waste stream at several different locations. These include manufacturing facilities, new construction sites, renovation activities, and when buildings are demolished or disassembled. Debris from construction sites may be encountered as large pieces that can be somewhat easily removed from other debris components. Methods for recycling gypsum from gypsum boards are known.

[0007] The method of making gypsum boards is well-known. For example, published European Patent Application No. 2641886 A2 describes a gypsum powder containing hemihydrate gypsum powder and type II anhydrite powder. Type II anhydrite is obtained by calcining dihydrate gypsum recovered from gypsum board waste. EP2641886 A2 further describes that some of the type II anhydrite can be replaced by dihydrate. Also, this dihydrate can be obtained from recycled materials. The powder of gypsum board waste is obtained by finely pulverizing the board waste and passing the pulverized product through a sieve to remove the board paper.

[0008] EP2030693 B1 also describes the recycling of gypsum products, in which a device (such as a sieve) for separating paper waste from the rest of the gypsum product waste is provided.

[0009] Published Patent Cooperation Treaty Application No. WO2009 / 064602 A1 describes wet pulverizing dihydrate together with a specific dispersant. The pulverized gypsum is used as a filler in cosmetics, paper, or coatings. However, WO2009 / 064602 A1 is not related to the recycling of gypsum product waste.

[0010] Published Patent Cooperation Treaty Application No. WO2019 / 001677A1 (Knauf GIPS KG) discloses a method for producing a gypsum slurry for forming gypsum products, particularly gypsum boards, preferably gypsum paper boards, comprising: a) providing a gypsum paper product comprising gypsum and a paper component, particularly a gypsum paper board, and / or a crushed part thereof; and b) wet-grinding the gypsum paper product and / or a crushed part thereof containing at least a part of the paper component to form a wet-ground gypsum paper component. The method decomposes (grinds) the gypsum paper product together with the paper component (i.e., does not remove the paper component in advance). It also preferably includes directly feeding the (new) gypsum product, preferably the (unfired) ground material, into the gypsum slurry.

[0011] In another method for recycling gypsum from gypsum boards, after separating the gypsum core, the board is typically ground to a particle size of about 300 μm or less (e.g., D50 of about 10 μm - 200 μm, e.g., 10 μm - 60 μm), then fired to dehydrate calcium sulfate dihydrate to calcium sulfate hemihydrate. This calcium sulfate hemihydrate can then be reused in new products.

[0012] U.S. Patent No. 10,570,062 discloses a method for making a gypsum plaster board in which the bander waste added to the gypsum slurry is obtained from the production process of an impregnated plaster board using a hydrophobizing agent, i.e., silicone oil.

[0013] Published Patent Cooperation Treaty Application No. WO2019 / 813144A1 teaches recycled gypsum having a foaming agent that is at least one alpha-sulfo fatty acid disalt to reduce the wet density of a composition having a recycled gypsum content of at least 0.5 wt%.

[0014] Japanese Patent Application Publication No. 09165244A discloses a gypsum plaster board material containing 3 wt% or less of a finely ground waste gypsum material. The finely ground waste gypsum material has a particle size of 1.0 - 4.0 m2 It is pulverized by the pulverization energy of 3 to 15 kw / gypsum board waste so that the BET specific surface area of / g exists.

[0015] U.S. Patent Application Publication No. 2016 / 0214895 discloses a method and apparatus for recycling gypsum board, which includes pulverizing raw materials into chunks and further pulverizing the materials with a rolling mill, reducing the size of the materials, and partially knocking off the gypsum from the backing paper. The materials are then sieved, and as a result, only the gypsum materials are deposited in the hopper. After a mixer assembly that mixes the recycled gypsum of various sizes into a certain mixture, such materials are passed through a roll press subsystem to densify such materials, and then a material of a known uniform composition suitable for cement production is generated. This recycled gypsum of this specific physical form factor can then be used in a significant proportion as a substitute for virgin gypsum in cement production. This method and apparatus are applicable to the recycling of both new and renovated gypsum-based building materials.

[0016] The above process is relatively simple, but when recycling gypsum board containing hydrophobic materials such as gypsum and siloxane, the recycling process becomes difficult. For example, attempts to recycle siloxane-containing gypsum have not been successful because siloxane-containing gypsum particles interfere with the hardening process of gypsum, especially when it is desirable to incorporate air bubbles into the gypsum board structure. Siloxane-containing gypsum particles prevent the incorporation (foaming) of air bubbles in the gypsum slurry. Therefore, these gypsum board products usually cannot be recycled and are discarded as waste.

[0017] Therefore, in this technical field, there is a need to develop an improved method for recycling gypsum from gypsum board, especially when recycling gypsum materials containing hydrophobic components. Summary of the Invention

[0018] An embodiment of the present invention is a method for making gypsum board, comprising A first plurality of particles comprising water, at least about 50 wt% calcium sulfate dihydrate, and about 0.05 wt% to about 10 wt% hydrophobic material, having a particle size distribution with a D50 particle size of about 200 μm to about 800 μm as determined using ASTM D6913-17 Method B, and a second plurality of particles comprising calcium sulfate hemihydrate and optionally one or more additives are combined to make an aqueous gypsum slurry, depositing a core layer comprising the aqueous gypsum slurry on a forming surface, hardening the core layer, thereby forming a hardened gypsum core, and providing a method.

[0019] Embodiments of the present invention typically combine a first plurality of particles comprising at least about 50 wt% calcium sulfate dihydrate and about 0.05 wt% to about 10 wt% hydrophobic material and having a D50 particle size of about 200 μm to about 800 μm with a second plurality of particles comprising calcium sulfate hemihydrate to form a combined mixture of calcium sulfate, add water to the combined mixture of calcium sulfate to make an aqueous gypsum slurry, depositing a core layer comprising the aqueous gypsum slurry on a forming surface, hardening the core layer, thereby forming a hardened gypsum core.

[0020] Gypsum board is a gypsum product having a board shape (i.e., in particular, at least substantially flat). Gypsum board typically has a rectangular shape. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The following figures are included to illustrate certain aspects of the present disclosure and should not be regarded as exclusive embodiments. As will be apparent to those skilled in the art and to those having the benefit of this disclosure, the disclosed subject matter is capable of considerable modification, alteration, combination, and equivalents in form and function.

[0022]

Figure 1

Figure 2

Figure 3

Figure 4

DETAILED DESCRIPTION OF THE INVENTION

[0023] The present invention includes methods that can be used to recycle waste gypsum materials such as gypsum board. The waste gypsum board can include a hydrophobic material such as is used in applications to improve the moisture resistance of the gypsum board.

[0024] In this description, as non - limiting examples of waste gypsum materials and products made from recycled gypsum, drywall (interior wall board) used in the construction of interior walls and ceilings is exemplified. For the purposes of this specification, drywall is typically defined as a panel (also known as a board) that includes a core of calcium sulfate dihydrate, typically containing additives, between sheets of typically front and back facer sheets. Typically, the facer sheets are made of paper or glass fiber mat, but facer sheets of other fiber sheets can also be used. However, the processes disclosed herein can be used to process and recycle gypsum from any gypsum board having a core layer of gypsum - containing material and to make building products of any gypsum board having a core layer of gypsum - containing material.

[0025] One skilled in the art may modify the methods described herein to process waste gypsum materials from interior wallboards having a gypsum core between paper facer sheets, exterior finish gypsum panels, gypsum tile backer boards, or other gypsum building panels. For example, a typical gypsum exterior finish panel for processing according to the present invention may include, from front to back, a first fiber mat and a gypsum core layer having front and back surfaces, the gypsum core layer having a thickness of from about 0.25 inches to about 1.25 inches, preferably from about 0.25 inches to about 1 inch, the first fiber mat being attached to the front surface of the gypsum core layer as a facer cover sheet, a second fiber mat being attached to the back surface of the gypsum core layer as a backer cover sheet. The gypsum core layer may contain more than about 50% by weight, preferably at least about 75% by weight, more preferably at least about 85% by weight of calcium sulfate dihydrate. The first fiber mat and the second fiber mat may include paper or a fibrous material (e.g., one or more of polymer fibers, glass fibers, and mineral fibers).

[0026] Waste gypsum materials can be obtained from various sources. Non-limiting examples include waste from manufacturing facilities, waste from new construction sites, renovation waste, and waste from the demolition or dismantling of buildings. Generally, waste gypsum materials include a gypsum-containing material, typically a layer or core, and one or more facer sheets. Waste gypsum materials containing calcium sulfate dihydrate include gypsum boards, such as interior drywall, exterior cladding panels, and tile backer boards. Also, waste materials containing gypsum include special gypsum board products that may include a glass fiber-reinforced gypsum core or may be externally coated with glass fibers to reinforce the board and enhance moisture resistance. Waste materials containing calcium sulfate dihydrate may also include components such as fibrous woven or non-woven layers containing paper, glass fibers, mineral fibers, polymers, etc. In particular, gypsum boards generally have a gypsum core and front and back facer sheets of paper, non-woven fiber mat, or fiber mesh. The fibers of the non-woven fiber mat, or fiber mesh are typically glass fibers, mineral fibers, or polymer fibers, and most typically glass fibers. Generally, the core layer of waste gypsum materials is more than 50% by weight of gypsum.

[0027] In one aspect, the present invention includes a method for converting a waste gypsum material containing a hydrophobic additive into gypsum suitable for reuse in new gypsum building materials. The resulting new gypsum building material includes up to 10 wt%, up to 20 wt%, up to 30 wt%, up to 40 wt%, up to 50 wt%, up to 60 wt%, up to 70 wt%, up to 80 wt%, up to 90 wt% of the waste gypsum material. Such a method may include providing a coarse waste gypsum material including pieces of gypsum board or other waste gypsum materials, wherein the gypsum-containing material of the coarse waste gypsum material includes more than about 50 wt% calcium sulfate dihydrate (e.g., gypsum), and from about 0.05 wt% to about 10 wt% of at least one hydrophobic additive. The amount of calcium sulfate dihydrate in the coarse waste gypsum material is preferably at least about 75 wt%, more preferably at least about 85 wt%. The coarse waste gypsum material is then processed to produce a first plurality of particles including the hydrophobic additive and calcium sulfate dihydrate. The first plurality of particles have a D50 particle size of from about 200 μm to about 800 μm. The particle size can be determined simply by passing the material through a sieve of appropriate size, as is well known in the art. The particle size distribution (e.g., D50) can also be determined using means known in the art. For example, one non-limiting example is disclosed in ASTM D6913 / D6913M-17 Method B, Standard Test Methods for Particle-Size Distribution (Gradation) of Soils Using Sieve Analysis.

[0028] The hydrophobic material additive in the waste gypsum material can be coated on the outer surface of the gypsum core and / or the first plurality of particles can be a constituent within the gypsum core that includes up to about 10 wt% of the hydrophobic material, such as from about 0.05 wt% to about 10 wt%, or from about 1 wt% to about 5 wt%. Thus, by weight, the solid layer of the gypsum core in the waste gypsum material can include up to about 10 wt% of the hydrophobic material, such as from about 0.05 wt% to about 10 wt%, or from about 1 wt% to about 5 wt%. For example, the lower limit of the hydrophobic material can be about 0.05 wt%, about 0.1 wt%, about 0.5 wt%, or about 1 wt% of the gypsum-containing material. For example, the upper limit of the hydrophobic material can be about 2 wt%, about 5 wt%, about 7 wt%, or about 10 wt% of the gypsum-containing material. A typical hydrophobic material is a siloxane or a wax. Thus, the hydrophobic additive in the waste gypsum material can be, for example, a siloxane-containing constituent. A hydrophobic material tends to repel water, cannot be mixed with water, and / or has limited wettability with water. It is the opposite of a hydrophilic material that has a tendency to mix, dissolve, and / or wet with water.

[0029] In another aspect, embodiments of the present invention include a method for using recycled gypsum containing a hydrophobic additive to manufacture a gypsum board. Such a method can include combining a first plurality of particles that include water, at least about 50 wt% calcium sulfate dihydrate, and from about 0.05 wt% to about 10 wt% of a hydrophobic material and have a particle size distribution with a D50 particle size of from about 200 μm to about 800 μm, and a second plurality of particles that include calcium sulfate hemihydrate to make an aqueous gypsum slurry, depositing a core layer that includes the aqueous gypsum slurry on a forming surface, and curing the core layer to thereby form a cured gypsum core.

[0030] Typically, the first plurality of particles comprising calcium sulfate dihydrate (uncalcined recycled gypsum) are from about 0.1 wt% to about 20 wt%, more typically from about 1 wt% to about 10 wt%, even more typically from about 2 wt% to about 7 wt%, and most typically from about 2 wt% to about 5 wt% of the total dry weight of the first plurality of particles and the second plurality of particles combined to form an aqueous gypsum slurry. For example, the first plurality of particles can be from about 1 wt% to about 5 wt%, or from about 2 wt% to about 4 wt% of the total dry weight of the first plurality of particles and the second plurality of particles. As used herein, "total dry weight" or "on a dry weight basis" refers to the weight of the mixture excluding any water constituents that may be present. "Water constituents" excludes water that may be present in the crystal structure of the gypsum. In contrast, "on a wet basis" includes water in the weight % calculation.

[0031] The uncalcined recycled gypsum and the second plurality of particles can be fed to a slurry mixer as separate streams and mixed with water to form an aqueous gypsum slurry. Alternatively, the uncalcined recycled gypsum and the second plurality of particles can be combined to form a combined gypsum stream, and then the combined gypsum stream can be fed to a slurry mixer as a separate stream and mixed with water to form an aqueous gypsum slurry. In either case, the aqueous gypsum slurry can be formed into a new gypsum material suitable for use as a building material. For example, new gypsum panels of various widths and thicknesses can be manufactured by methods known in the art. Water, and optionally one or more additives, are supplied to make the aqueous gypsum slurry separately from, or together with, one or more of the first plurality of particles and the second plurality of particles.

[0032] Preferably, the method includes combining a first plurality of particles comprising a hydrophobic additive and calcium sulfate dihydrate, the first plurality of particles having a D50 particle size of about 200 μm to about 800 μm (referred to herein as "the first plurality of particles"), with a second plurality of particles comprising calcium sulfate hemihydrate to form a combined gypsum mixture.

[0033] In particular, the first plurality of particles are not fired prior to combination with the second plurality of particles to form the combined gypsum mixture. Thus, as used herein, "unfired recycled gypsum" refers to this first plurality of particles comprising calcium sulfate dihydrate and a hydrophobic additive. Calcium sulfate Half The second plurality of particles comprising the hydrate can have a typical D50 particle size in drywall manufacturing (e.g., from about 10 μm to about 100 μm), can be obtained from raw mined gypsum, synthetic gypsum (e.g., waste materials from flue gas desulfurization), or can be recycled and fired.

[0034] Embodiments of the present invention can include using a foaming agent. In some embodiments, the foaming agent does not include an alpha-sulfo fatty acid disalt.

[0035] FIG. 1 illustrates one way in which waste gypsum materials can be processed. The gypsum waste can be residues, waste, or unused / useless gypsum board products and / or crushed portions thereof. The crushed portions can be portions of accidentally and / or intentionally crushed gypsum products, particularly gypsum board, or (larger) crushed portions thereof. The gypsum waste can include a gypsum layer of the gypsum material, can contain at least one facer sheet, or may not, and the gypsum layer includes at least about 50 wt% calcium sulfate dihydrate and from about 0.05 wt% to about 10 wt% hydrophobic material. Generally, suitable gypsum waste that can be recycled according to the processes disclosed herein has a total organic content of about 6.4 wt% or less, together with a total paper fiber content not exceeding about 5.5 wt%.

[0036] When obtained, the feed of gypsum waste such as gypsum drywall and / or its crushed parts is obtained as or processed to be coarse gypsum, i.e., large chunks and coarse fragments, and thus can be more easily processed by crushing the larger fragments into smaller ones. The crushing can be done by methods known in the art. For example, the incoming material can be sized down using a crusher, a crusher, a bucket crusher, an excavator with a grapple, or simply by running it through a front-end loader. Optionally, non-gypsum board materials (e.g., nails and / or other debris) can be separated at 104 to ensure that these materials do not proceed to the next step of the process. The coarse gypsum fragments 106 are then fed to the grinding stage 112, where the coarse gypsum fragments 106 can be crushed into gypsum particles 116. These coarse fragments 106 can be, for example, fragments less than about 10 inches, typically less than about 5 inches, and preferably less than about 2 inches in the crushing stage 104. For example, the gypsum waste 106 can be crushed to be a coarse material having a size of less than about 5 inches, e.g., 0.5 inches to 5 inches, or about 0.5 inches to 2 inches.

[0037] The gypsum waste 102 typically has a front and / or rear facer sheet. Typical facer sheets are paper facer sheets, or woven or non-woven fiber mat facer sheets, e.g., woven or non-woven glass mats. Crushing 104 can separate some facer materials (e.g., paper, glass mat) from the coarse gypsum fragments (e.g., the gypsum core of the gypsum board). However, some or all of the separated facer materials 114 are typically removed as separated facer sheets by suitable shearing and grinding machines in the grinding stage 112, such as a separator having a paddle blade screw conveyor surrounded by a grinding screen, which removes the facer sheet for disposal or reuse and grinds the remaining gypsum into gypsum particles 116.

[0038] The grinding stage 112 can be operated under conditions sufficient to remove the face sheet and impart a D50 particle size of from about 200 μm to about 800 μm, preferably from about 300 μm to about 500 μm, for example about 400 μm, to most of the gypsum particles 116 exiting the grinding stage 112. Any grinding device can be used, and one skilled in the art will be able to vary the experimental parameters of the mechanical sizing device and determine the appropriate speed, force, and time to produce gypsum particles 116 having the desired particle size. For example, the above-described separator having a paddle blade screw conveyor surrounded by a grinding screen can be used. The grinder 112 is provided with one or more screens 113 that allow particles having the desired size (e.g., 200 μm to 800 μm) to pass through the screen 113 and can be conveyed to the collection bin 118 as a plurality of recycled gypsum particles 116 having a D50 particle size of from about 200 μm to about 800 μm.

[0039] The recycled gypsum 116 can then be conveyed to a drywall manufacturing assembly line as shown in FIG. 2. FIG. 2 shows an exemplary wallboard assembly line 200 having a first hopper 206 for receiving recycled unfired gypsum 116 from the process shown in FIG. 1. The second hopper 202 can contain calcium sulfate hemihydrate obtained either from raw gypsum (“virgin gypsum”) or as calcined recycled gypsum. The recycled gypsum 116, calcium sulfate hemihydrate (virgin dehydrated gypsum or calcined recycled gypsum) 203 can be conveyed through conduit 208 to mixer 212 together with any desired dry additive 204. The introduction of each component into conduit 208 can be facilitated by a metering supply device (not shown). Optionally and alternatively, the calcium sulfate hemihydrate 203 can be supplied directly to the mixer 212 through a second conduit (not shown in FIG. 2) separate from the conduit 208 that conveys the recycled gypsum 116 to the mixer. One skilled in the art will be able to visualize and readily adopt this alternative manufacturing design. Water 210 and any desired wetting additive can be added to the mixer 212 to produce an aqueous gypsum slurry.

[0040] Alternatively, the forming table 218 can supply a continuous forming surface 216 (e.g., paper, woven fiber, or non-woven fiber suitable as a front or back facer sheet) under the discharge port 214 of the mixer 212. The discharge port 214 deposits and spreads the gypsum slurry 220 onto the forming surface 216. The gypsum slurry 220, when cured, becomes the gypsum core of the gypsum board. Air or bubbles can be added to the aqueous gypsum slurry passing through the discharge port 214 (e.g., a gate as described in, for example, U.S. Patent Nos. 5,683,635 and 6,494,609) by injecting air or bubbles through the conduit 232.

[0041] Downstream of the discharge port 214, a continuous facer sheet layer 222 (e.g., paper, woven fiber, or non-woven fiber suitable as a front or back facer sheet) is placed on the gypsum slurry 220 to create a layered preformed assembly 225. The layered preformed assembly 225 is cut to a desired length using a cutting tool 224 (e.g., a knife) to become a preformed panel 226. The preformed panel 226 can then pass through a kiln 228 to dry the aqueous gypsum slurry and cure the preformed gypsum panel 226, emerging as a fully cured gypsum panel 230. The fully cured gypsum panel includes, as a front surface, the forming surface 216, a core gypsum layer formed from the gypsum slurry 220, and a back surface formed from the backing layer 222.

[0042] It is also common in the manufacture of cementitious building panels such as gypsum panels for the core gypsum layer to further include one or more dense thin layers of the gypsum slurry, referred to herein as a "skim layer". Thus, a relatively denser layer of the gypsum slurry from the skim layer can be deposited on the forming surface 316 (FIG. 3) before depositing a relatively less dense gypsum slurry (referred to herein as "primary gypsum slurry") from most of the gypsum core to form the skim layer.

[0043] Figure 3, in which all like numbers represent like elements as shown in Figure 2, shows such a process 300. A portion of the gypsum slurry discharged from the mixer 212 is diverted through one or more pressurized slurry lines 303, 305, exits through a smaller outlet port, and may form a first skim layer gypsum slurry 315 on the forming surface 316. Additives can be injected in wet form through injection ports into the pressurized slurry lines 303, 305 as needed. The pressurized slurry lines 303, 305 are desirably long enough to allow for uniform mixing of the slurry and additives. The forming surface 316 can be, for example, paper such as used for laminated tilebacker panels or exterior siding panels, or a non-woven glass fiber cover sheet. The primary gypsum slurry 320, which upon curing forms most of the core of the gypsum board, can be applied over the first skim layer gypsum slurry 315 through the discharge port 214. As described above with respect to Figure 2, the primary gypsum slurry 320 can be foamed by injecting foam or air through the conduit 232. Optionally, a second skim layer gypsum slurry 317 can be deposited over the primary gypsum slurry 320. A second layer of backing (facer) material 222, such as paper or non-woven glass fiber cover sheet material, is applied to the second skim layer gypsum slurry 317 (or to the core gypsum slurry if the second skim layer is not desired), and the layer can be compressed through the forming station to the desired total thickness (e.g., a thickness of about 0.25 inches to about 1.5 inches, preferably about 0.25 inches to about 1.0 inches). The resulting structure is the preformed gypsum board 325.

[0044] When the primary gypsum slurry 320 for the core layer is foamed, the first and second skim layer gypsum slurries 315, 317 are either not foamed or foamed to a lesser extent, becoming relatively dense and thin compared to the foamed primary gypsum slurry. Thus, the aqueous slurries for the first and second skim layer gypsum slurries may or may not be exposed to air or bubbles that can be added to the primary gypsum slurry 320. The primary gypsum slurry 320 can be foamed by injecting air or bubbles through conduit 232 into the aqueous gypsum slurry passing through discharge port 214.

[0045] When foamed, a portion of the gypsum core resulting from the cured foamed primary gypsum slurry can have a total air bubble volume of about 30% to about 90% by volume, preferably about 45% to about 80% by volume of air. The first skim layer and the second skim layer (if present) obtained by curing the first and second skim layer gypsum slurries can have a total air bubble volume of about 30% by volume or less, preferably about 10% by volume or less. The air bubbles in the gypsum core can have an average cross-sectional diameter of less than 1.5 mm, preferably about 0.5 to about 0.8 mm, more preferably about 0.3 mm.

[0046] Typically, the first and second skim slurries 315, 317 have the same composition and density. However, if desired, the first and second skim layer slurries 315, 317 can have different compositions and / or densities. FIG. 3 shows all the gypsum slurries 320, 315, 317 coming from the same mixer 212. However, each gypsum slurry 320, 315, 317 can come from different mixers so as to have different properties such as different densities.

[0047] The calcium sulfate particles in each of the gypsum slurries 320, 315, 317 can react with water when combined with water and can be cured as the gypsum panel preform 325 moves along the production line. The gypsum panel preform 325 can be dried and cut along the line into segments 326 of a predetermined dimension at a point where the panel preform 325 of the gypsum panel is sufficiently cured. The segment 326 can be turned over, dried 228 (e.g., in a kiln), with excess water removed and processed to provide a final laminated wallboard 330 of the desired dimension. The combined thickness of the gypsum cores (including optional skim coats) obtained from the cured gypsum slurries 320, 315, 317 can generally be from about 0.25 inches to about 1.5 inches. The combined density can be from about 15 pounds per cubic foot to about 65 pounds per cubic foot, more typically from 25 pounds per cubic foot to about 65 pounds per cubic foot, for example from 25 pounds per cubic foot to 55 pounds per cubic foot.

[0048] The gypsum material can be processed in the same manner as described above, bypassing any firing, thereby reducing the overall energy required to recycle the gypsum.

[0049] Advantageously, the method described herein enables the recycling of gypsum materials that would otherwise not be suitable for reuse in new products. In particular, the gypsum particles, even after being reduced in size, still contain one or more of the hydrophobic additives present in the solid layer in which the particles were formed and may be coated, which has previously been incompatible in this specification for incorporation into aqueous gypsum slurries for drywall manufacture, particularly in drywall containing foam constituents. Previous attempts have revealed that hydrophobic-containing gypsum particles break the walls of air bubbles and the stability of the slurry is lost. Surprisingly, it has been found that using a larger particle size than typically used in gypsum recycling, i.e., a D50 particle size of about 200 μm to about 1000 μm, preferably about 200 μm to about 800 μm, reduces much of the incompatibility. Furthermore, these particles do not need to be fired. Thus, recycled unfired gypsum has been found to be incorporated into aqueous gypsum slurries at significant percentages (e.g., up to about 10 wt% or more), thereby being effectively recycled thereto before unusable gypsum waste.

[0050] In particular, gypsum drywall containing hydrophobic constituents, which would otherwise be discarded, can be recycled into new drywall having properties conforming to ASTM standard C1396 / C1396M-17. Various properties such as flexural strength, hardness (core, ends, and edges), nail pullout resistance, humidified deflection, end squareness, nominal thickness, depth of dents or tapered ends, width, length, water resistance of core-treated water-repellent gypsum panel products, and surface water resistance of gypsum panel products having water-repellent surfaces can be determined as described in ASTM C473-19.

[0051] All documents described in this specification are hereby incorporated by reference for the purposes of all jurisdictions in which such practices are permitted, including any priority documents and / or test procedures to the extent they are not inconsistent with this text. As will be apparent from the foregoing general description and the specific embodiments, while forms of the present disclosure have been illustrated and described, various changes can be made without departing from the spirit and scope of the present disclosure. Accordingly, it is not intended that the present disclosure be limited thereby. For example, the compositions described herein may or may not include components or compositions not expressly recited or disclosed herein. Any method may or may not include any steps not recited or disclosed herein. Similarly, the term "comprising" is considered to be synonymous with the term "including". Whenever a transitional phrase "comprising" is attached to a method, composition, element, or group of elements, the inventors also intend, and vice versa, the same composition or group of elements having a transitional phrase "consisting essentially of", "consisting of", "selected from the group consisting of", or "is" before the reference to the composition, element, or elements.

[0052] Unless otherwise indicated, all numbers expressing quantities of ingredients, properties such as molecular weights, reaction conditions, and the like, used in the specification and the associated claims are to be understood as being modified in all instances by the term "about". Accordingly, unless indicated to the contrary, the numerical parameters set forth in the following specification and attached claims are approximations that may vary depending upon the desired properties sought to be obtained by the embodiments of the present invention. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the reported number of significant digits and by applying ordinary rounding methods.

[0053] When a numerical range with a lower limit and an upper limit is disclosed, any numerical value and any included range that fall within that range are always specifically disclosed. In particular, all ranges of values disclosed herein (in the form of "about a to about b", or equivalently "from approximately a to b", or equivalently "from approximately a - b") are to be understood as indicating all numerical values and ranges encompassed by the broader range of values. Also, the terms of the claims have their plain and ordinary meaning unless otherwise expressly and clearly defined by the patentee. Further, the indefinite articles "a" or "an" used in the claims are defined herein to mean one or more of the elements they introduce.

[0054] As used in the present disclosure, "NP" refers to the nail pull - out strength.

[0055] "MT" refers to a product containing siloxane.

[0056] "GM" means gypsum obtained from gypsum waste having a gypsum core containing siloxane and coated with glass fibers. More specifically, the type "GM" gypsum particles described in the non - limiting examples of the present disclosure had the following particle size distribution characteristics: approximately 15.2 wt% of the particles were larger than 840 μm, approximately 52.2 wt% of the particles were sized from 300 μm to 840 μm, approximately 19.0 wt% of the particles were sized from 150 μm to 300 μm, and approximately 12.0 wt% of the particles were smaller than 150 μm. These particles had a D50 particle size in the range of about 200 μm to about 800 μm.

[0057] One or more exemplary embodiments are presented herein. For clarity, not all functions of a physical implementation are described or shown in this application. In developing a physical embodiment of the present disclosure, it is understood that numerous implementation-specific decisions must be made to achieve the developer's goals, such as compliance with system-related, business-related, government-related, and other constraints, which vary by implementation and over time. The developer's efforts may be time-consuming, but such efforts are, however, routine work for those skilled in the art and will be beneficial to the present disclosure.

[0058] To facilitate a better understanding of embodiments of the present invention, the following examples of preferred or representative embodiments are provided. The following examples should not be read to limit or define the scope of the present invention.

[0059] The terms of the present invention The following terms disclose various aspects of the present invention.

[0060] Clause 1. A method for making a gypsum board, comprising: combining a first plurality of particles comprising water, at least about 50 wt% calcium sulfate dihydrate, and about 0.05 wt% to about 10 wt% hydrophobic material and having a D50 particle size of about 200 μm to about 800 μm, and a second plurality of particles comprising calcium sulfate hemihydrate to form an aqueous gypsum slurry; depositing a core layer comprising the aqueous gypsum slurry on a forming surface; hardening the core layer to thereby form a hardened gypsum core.

[0061] Clause 2. The method according to Clause 1, wherein the first plurality of particles are combined with the second plurality of particles to form a combined mixture of calcium sulfate, and water is added to the combined mixture of calcium sulfate to form an aqueous gypsum slurry.

[0062] Clause 3. The method according to clause 1, wherein a plurality of first particles are combined with a plurality of second particles to form a combined dry mixture of calcium sulfate, and water is added to the combined dry mixture of calcium sulfate to make an aqueous gypsum slurry.

[0063] Clause 4. The method according to any one of clauses 1 to 3, wherein the hydrophobic material comprises siloxane.

[0064] Clause 5. The method according to any one of clauses 1 to 3, wherein the hydrophobic material comprises wax.

[0065] Clause 6. The method according to any one of clauses 1 to 3, wherein the hydrophobic material comprises one or more of siloxane, wax, and resin.

[0066] Clause 7. The method according to any one of the preceding clauses, wherein the plurality of first particles have a D50 particle size of about 300 μm to about 500 μm.

[0067] Clause 8. A gypsum waste (typically, a gypsum board and / or a crushed part thereof) containing a gypsum feed material, wherein the gypsum feed material comprises at least about 50 wt% of calcium sulfate dihydrate and about 0.05 wt% to about 10 wt% of a hydrophobic material, and further comprising subjecting the gypsum waste to a size reduction process to generate a plurality of first particles, the method according to any one of the preceding clauses.

[0068] Clause 9. The method according to clause 8, wherein the size reduction process comprises crushing the gypsum waste to form fragments having a dimension of 10 inches or less, preferably 5 inches or less, and pulverizing the fragments to generate a plurality of first particles.

[0069] Clause 10. The method according to any one of the preceding clauses, wherein the gypsum feed material comprises a gypsum layer and at least one facer sheet, the gypsum layer comprises at least about 50 wt% of calcium sulfate dihydrate and about 0.05 wt% to about 10 wt% of a hydrophobic material, and the gypsum feed material comprises a gypsum board containing at least one facer sheet.

[0070] Clause 11. The method according to claim 10, wherein at least one facer sheet comprises at least one of a glass mat facer sheet or a paper facer sheet.

[0071] Clause 12. The method according to clause 11, wherein the size reduction process at least partially removes or completely removes at least one facer sheet from the gypsum layer.

[0072] Clause 13. The method according to clause 11, wherein the size reduction process comprises crushing the gypsum waste to form fragments having a dimension of 10 inches or less, preferably 5 inches or less, and grinding the fragments to a D50 particle size of about 200 μm to about 800 μm, preferably about 300 μm to about 500 μm, and removing at least one facer sheet from the gypsum layer.

[0073] Clause 14. The method according to any one of the preceding clauses, wherein the hardened gypsum core contains gas bubbles.

[0074] Clause 15. The method according to any one of the preceding clauses, wherein the hardened gypsum core contains gas bubbles, and the gas bubbles have an average cross-sectional diameter of less than 1.5 mm, about 0.5 to about 0.8 mm, about 0.3 mm, or about 0.3 mm or less.

[0075] Clause 16. Depositing a core layer on the forming surface comprises depositing a first portion of an aqueous gypsum slurry as a skim layer on the forming surface, depositing a second portion of the aqueous gypsum slurry as a primary gypsum layer on the skim layer, drying the skim layer and the primary gypsum layer, thereby forming a hardened gypsum core, and the method according to any one of the preceding clauses.

[0076] Clause 17. The method according to any one of the preceding clauses, wherein the aqueous gypsum slurry comprises from about 0.1 wt% to about 20 wt% of the first plurality of particles, based on the combined dry weight of the first plurality of particles and the second plurality of particles.

[0077] Clause 18. The method according to any one of the preceding clauses, wherein the hydrophobic material comprises a siloxane, and the first plurality of particles comprises from about 0.05 wt% to about 5 wt%, typically from 0.1 wt% to about 3 wt%, of the siloxane.

[0078] Clause 19. The method according to any one of the preceding clauses, wherein the hydrophobic material comprises a wax, and the first plurality of particles comprises from about 0.5 wt% to about 10 wt%, typically from 1 wt% to about 7 wt%, for example from about 3 wt% to about 7 wt%, of the wax.

[0079] Clause 20. The method according to any one of the preceding clauses, wherein the aqueous gypsum slurry comprises from about 1 wt% to about 10 wt% of the first plurality of particles, based on the combined dry weight of the first plurality of particles and the second plurality of particles.

[0080] Clause 21. The method according to any one of the preceding clauses, wherein the aqueous gypsum slurry comprises from about 2 wt% to about 7 wt% of the first plurality of particles, based on the combined dry weight of the first plurality of particles and the second plurality of particles.

[0081] Clause 22. The method according to any one of the preceding clauses, wherein the aqueous gypsum slurry comprises from about 2 wt% to about 5 wt% of the first plurality of particles, based on the combined dry weight of the first plurality of particles and the second plurality of particles.

[0082] Clause 23. The method according to any one of the preceding clauses, further comprising adding air thereto before depositing the aqueous gypsum slurry.

[0083] Clause 24. The method according to any one of the preceding clauses, wherein the hardened gypsum core has a total air volume of from about 30 vol% to about 90 vol%.

[0084] The method according to clause 24, wherein the total air volume of the hardened gypsum core is from about 45% by volume to about 80% by volume.

[0085] The method according to any one of the preceding clauses, wherein the hardened skim layer has a total air volume of about 30% by volume or less.

[0086] The method according to any one of the preceding clauses, wherein the hardened skim layer has a total pore volume of about 10% by volume or less.

[0087] The method according to any one of the preceding clauses, wherein at least about 98% by weight of the first plurality of particles have a particle size of from about 100 μm to about 3000 μm.

[0088] A method for making a gypsum board, comprising: combining a first plurality of particles comprising water, at least about 50% by weight of calcium sulfate dihydrate, and from about 0.05% by weight to about 10% by weight of a hydrophobic material, wherein at least about 98% by weight of the first plurality of particles have a particle size of from about 100 μm to about 3000 μm, and a second plurality of particles comprising calcium sulfate hemihydrate to form an aqueous gypsum slurry; depositing a core layer comprising the aqueous gypsum slurry on a forming surface; hardening the core layer to thereby form a hardened gypsum core.

[0089] The method according to clause 29, wherein the first plurality of particles are combined with the second plurality of particles to form a combined mixture of calcium sulfate, and water is added to the combined mixture of calcium sulfate to form an aqueous gypsum slurry.

[0090] The method according to clause 30, wherein the first plurality of particles are combined with the second plurality of particles to form a combined dry mixture of calcium sulfate, and water is added to the combined dry mixture of calcium sulfate to form an aqueous gypsum slurry.

[0091] Clause 32. The method according to any one of Clauses 29 to 32, wherein the hydrophobic material comprises one or more of siloxane, wax, and resin.

[0092] Clause 33. The method according to any one of Clauses 29 to 32, wherein the aqueous gypsum slurry comprises from about 0.1 wt% to about 20 wt% of the first plurality of particles, based on the combined dry weight of the first plurality of particles and the second plurality of particles.

[0093] Clause 34. The method according to any one of Clauses 29 to 32, wherein the aqueous gypsum slurry comprises from about 1 wt% to about 10 wt% of the first plurality of particles, based on the combined dry weight of the first plurality of particles and the second plurality of particles.

[0094] Clause 35. The method according to any one of Clauses 29 to 34, wherein the hydrophobic material comprises siloxane and the first plurality of particles comprises from about 0.05 wt% to about 5 wt%, typically from 0.1 wt% to about 3 wt% of the siloxane.

[0095] Clause 36. The method according to any one of Clauses 29 to 34, wherein the hydrophobic material comprises wax and the first plurality of particles comprises from about 0.5 wt% to about 10 wt%, typically from 1 wt% to about 7 wt%, for example from about 3 wt% to about 7 wt% of the wax.

Examples

[0096] Table 1 below describes the manufacture of four different drywall products using various amounts of siloxane-containing uncalcined recycled gypsum. Two types of waste products were processed to obtain uncalcined recycled gypsum.

[0097] Type "MT" gypsum was obtained from gypsum waste having a gypsum core coated with paper and containing siloxane. More specifically, the Type "MT" gypsum particles had the following particle size distribution characteristics: Approximately 23.6% by weight of the particles were larger than 840 μm, approximately 41.1% by weight of the particles were sized between 300 μm and 840 μm, approximately 20.0% by weight of the particles were sized between 150 μm and 300 μm, and approximately 14.2% by weight of the particles were smaller than 150 μm. Trace amounts (e.g., 1.5% by weight or less) of paper and / or glass fibers can also be mixed with the plurality of recycled gypsum. These particles had a D50 particle size in the range of approximately 200 μm to approximately 800 μm.

[0098] Type "GM" gypsum was obtained from gypsum waste having a gypsum core coated with fiberglass and containing siloxane. More specifically, the Type "GM" gypsum particles had the following particle size distribution characteristics: Approximately 15.2% by weight of the particles were larger than 840 μm, approximately 52.2% by weight of the particles were sized between 300 μm and 840 μm, approximately 19.0% by weight of the particles were sized between 150 μm and 300 μm, and approximately 12.0% by weight of the particles were smaller than 150 μm. These particles had a D50 particle size in the range of approximately 200 μm to approximately 800 μm.

[0099] The manufactured product "A" is a 5 / 8-inch fire-resistant fiberglass-reinforced Type X gypsum board wrapped in paper. Product "B" is a 5 / 8-inch fire-resistant fiberglass-reinforced Type X gypsum board wrapped in moisture- and mold-resistant paper. Product "C" is a 1 / 2-inch lightweight gypsum panel. Product "D" is a 1-inch fire-resistant fiberglass-reinforced Type X gypsum board wrapped in fiberglass.

Table 1

[0100] The above products "A", "B", "C", and "D" were successfully prepared according to the characteristics described in Table 2 below.

Table 2

[0101] Previously, attempts to use hydrophobic-containing gypsum particles failed due to the defoaming properties of the hydrophobic-containing gypsum particles, which disrupted the gypsum slurries of 220 in FIG. 2 and 320 in FIG. 3, prevented the formation of the preformed gypsum cores 225 in FIGS. 2 and 3, and as a result, halted the drywall manufacturing process. The disrupted gypsum cores have a total pore (or air bubble) volume of less than about 30%. During the manufacture of these examples, when recycled gypsum particles having a particle size in the range of 200 μm to 800 μm were used, no obvious defoaming and disintegration of the gypsum cores were observed when manufacturing product boards of types "A", "B", "C", and "D". In some cases, increasing the total soap that increases the strength of the walls of the air bubbles effectively offsets any defoaming action by the hydrophobic-containing gypsum particles, prevents the disintegration of the gypsum core, and allows for the continuous operation of the drywall manufacturing process.

[0102] After drying, the properties of the boards obtained in the different trials above had no visible defects compared to the controls (i.e., Example Nos. 1, 4, 7, and 10). As shown in Table 1, the boards made using recycled uncalcined gypsum essentially had the same properties such as nail pullout as the boards made using calcined materials.

[0103] FIG. 4 shows the nail pullout strength of the boards made in accordance with the present invention. Gypsum boards (including the core and the upper and lower cover sheets) made with a thickness of 1 / 2 inch were prepared using various amounts of uncalcined waste. This figure shows that the nail pullout strength is not statistically different from the control. The control contains a first plurality of 0% and has a weight of 1360 lbs per 1000 square feet of 1 / 2 inch boards.

[0104] Accordingly, the present disclosure is well adapted to attain the stated objects and advantages, as well as those inherent therein.

[0105] The above specific disclosure is merely illustrative, and the present disclosure can be modified and implemented in different but equivalent manners that will be apparent to those skilled in the art and who benefit from the teachings herein. Further, except as set forth in the following claims, it is not intended to be limited to the details of the structures or designs shown herein. [Appendix] [Appendix 1] A method for making a gypsum board, comprising: combining a first plurality of particles comprising water, at least about 50 wt% calcium sulfate dihydrate, and about 0.05 wt% to about 10 wt% hydrophobic material, said first plurality of particles having a D50 particle size of about 200 μm to about 800 μm, and a second plurality of particles comprising calcium sulfate hemihydrate to make an aqueous gypsum slurry; depositing a core layer comprising said aqueous gypsum slurry on a forming surface; hardening said core layer, thereby forming a hardened gypsum core. [Appendix 2] combining said first plurality of particles with said second plurality of particles to form a combined mixture of calcium sulfate; adding said water to said combined mixture of calcium sulfate to make said aqueous gypsum slurry, the method according to Appendix 1. [Appendix 3] combining said first plurality of particles with said second plurality of particles to form a combined dry mixture of calcium sulfate, adding said water to said combined dry mixture of calcium sulfate to make said aqueous gypsum slurry, the method according to Appendix 1. [Appendix 4] The method according to Appendix 1, wherein said hydrophobic material comprises one or more of siloxane, wax, and resin. [Appendix 5] The method according to Appendix 1, wherein said first plurality of particles have a D50 particle size of about 300 μm to about 500 μm. [Appendix 6] subjecting a gypsum waste comprising a gypsum feed material to a size reduction process to produce said first plurality of particles, said gypsum feed material comprising: A) at least about 50 wt% calcium sulfate dihydrate, and B) a hydrophobic material; said gypsum feed material comprising a gypsum layer and optionally at least one facer sheet, said gypsum layer comprising at least about 50 wt% calcium sulfate dihydrate and about 0.05 wt% to about 10 wt% hydrophobic material, said gypsum feed material comprising a gypsum board comprising at least one facer sheet, further comprising subjecting. [Appendix 7] The method according to Appendix 6, wherein said at least one facer sheet comprises at least one of a glass mat facer sheet and a paper facer sheet, and said size reduction process at least partially removes said at least one facer sheet from said gypsum layer. [Appendix 8] The method according to Appendix 1, wherein the aqueous gypsum slurry contains from about 0.1% to about 20% by weight of the first plurality of particles based on the combined dry weight of the first plurality of particles and the second plurality of particles. [Appendix 9] The method according to Appendix 1, wherein the aqueous gypsum slurry contains from about 1% to about 10% by weight of the first plurality of particles based on the combined dry weight of the first plurality of particles and the second plurality of particles. [Appendix 10] A method for making a gypsum board, combining a first plurality of particles comprising water, at least about 50% by weight of calcium sulfate dihydrate, and from about 0.05% to about 10% by weight of a hydrophobic material, wherein at least about 98% by weight of the first plurality of particles have a particle size of from about 100 μm to about 3000 μm, and a second plurality of particles comprising calcium sulfate hemihydrate to form an aqueous gypsum slurry; depositing a core layer comprising the aqueous gypsum slurry on a forming surface; hardening the core layer to thereby form a hardened gypsum core.

Claims

1. A method for making a gypsum board, comprising: Combining water, a first plurality of particles, and a second plurality of particles to form an aqueous gypsum slurry, wherein the first plurality of particles comprises at least 50 wt% calcium sulfate dihydrate and 0.05 wt% to 10 wt% hydrophobic material, the first plurality of particles has a D50 particle size of 200 μm to 800 μm, and the second plurality of particles comprises calcium sulfate hemihydrate, to form the aqueous gypsum slurry; Depositing a core layer comprising the aqueous gypsum slurry on a forming surface; Curing the core layer to thereby form a cured gypsum core; A method comprising the above.

2. Combining the first plurality of particles with the second plurality of particles to form a combined mixture of calcium sulfate; Adding the water to the combined mixture of calcium sulfate to form the aqueous gypsum slurry, according to the method of Claim 1.

3. Combining the first plurality of particles with the second plurality of particles to form a combined dry mixture of calcium sulfate, and adding the water to the combined dry mixture of calcium sulfate to form the aqueous gypsum slurry, according to the method of Claim 1.

4. The method of Claim 1, wherein the hydrophobic material comprises one or more of siloxane, wax, and resin.

5. The method of Claim 1, wherein the first plurality of particles has a D50 particle size of 300 μm to 500 μm.

6. To produce the first plurality of particles, subjecting a gypsum waste material comprising a gypsum feed material to a size reduction process, wherein The gypsum feed material A) comprises at least 50 wt% calcium sulfate dihydrate, and B) comprises a hydrophobic material, The gypsum feed material comprises a gypsum layer and optionally at least one facer sheet, the gypsum layer comprises at least 50 wt% calcium sulfate dihydrate and 0.05 wt% to 10 wt% hydrophobic material, and the gypsum feed material comprises a gypsum board comprising at least one facer sheet; The method of Claim 1, further comprising subjecting the above.

7. The method according to claim 6, wherein the at least one facer sheet includes at least one of a glass mat facer sheet and a paper facer sheet, and the size reduction process at least partially removes the at least one facer sheet from the gypsum layer.

8. The method according to claim 1, wherein the aqueous gypsum slurry includes 0.1 wt% to 20 wt% of the first plurality of particles based on the combined dry weight of the first plurality of particles and the second plurality of particles.

9. The method according to claim 1, wherein the aqueous gypsum slurry includes 1 wt% to 10 wt% of the first plurality of particles based on the combined dry weight of the first plurality of particles and the second plurality of particles.

10. A method for making a gypsum board, comprising: combining water, a first plurality of particles, and a second plurality of particles to make an aqueous gypsum slurry, wherein the first plurality of particles includes at least 50 wt% calcium sulfate dihydrate and 0.05 wt% to 10 wt% hydrophobic material, at least 98 wt% of the first plurality of particles have a particle size of 100 μm to 3000 μm, and the second plurality of particles includes calcium sulfate hemihydrate, to make an aqueous gypsum slurry; depositing a core layer including the aqueous gypsum slurry on a forming surface; hardening the core layer, thereby forming a hardened gypsum core; and including.

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