METHODS FOR RECOVERING GYPSUM PANELS CONTAINING HYDROPHOBIC MATERIALS AND THEIR USE

Abstract

A method for preparing a gypsum board comprising: combining a first plurality of particles comprising at least approximately 50 wt% of calcium sulfate dihydrate and from approximately 0.05 wt% to approximately 10 wt% of hydrophobic material and having a D50 particle size of approximately 200 µm to approximately 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 prepare an aqueous gypsum slurry; depositing a core layer comprising the aqueous gypsum slurry onto a molding surface; and allowing the core layer to set, thereby forming a set gypsum core.

Description

Methods for recovering plasterboard containing hydrophobic materials and their use FIELD OF INVENTION This description relates to methods of reusing plasterboard waste. BACKGROUND OF THE INVENTION In building construction, one of the most common building elements is gypsum board, also known as drywall, gypsum building panels, drywall, or plasterboard, used in the construction of walls and / or ceilings. Walls made from gypsum board are traditionally constructed by attaching the panels to wood studs or metal frames and treating the joints between adjacent panels with a specially prepared adhesive called joint compound. Gypsum board easily conforms to walls of unusual size and can be shaped around structural elements such as beams or pipes. The side edges of gypsum board panels are tapered, allowing joint compound to be applied to the joint between adjacent panels, creating a monolithic finished surface. Gypsum board is made primarily from gypsum, unlike cement board which is primarily Ref. 338628 a cement, such as Portland cement. In particular, gypsum boards are composed primarily of calcium sulfate dihydrate. Gypsum boards are made by reacting water and stucco (calcium sulfate hemihydrate) such that the calcium sulfate hemihydrate sets to form calcium sulfate dihydrate (gypsum). Stucco is made by calcining gypsum and is usually composed primarily of calcium sulfate hemihydrate and may also contain anhydrous calcium sulfate. Calcium sulfate hemihydrate is produced by calcining calcium sulfate dihydrate to partially dehydrate the calcium sulfate dihydrate. When stucco is mixed with water, the calcium sulfate hemihydrate particles react and rehydrate to become set gypsum. The method of manufacturing gypsum board typically involves depositing an aqueous gypsum slurry (e.g., a mixture containing stucco and water). Optionally, one or more additives may be added to the slurry. Additives may include, for example, retarders, accelerators, foaming agents, wet strength enhancing materials, biocides, sag resistant ingredients, cellulose fibers, glass fibers, flame retardants, binders, hydrophobic ingredients, dust mitigants, starches, as well as other enhancing ingredients or materials known in the art.The slurry is normally deposited onto a sheet of moving paper facing or continuous fiber mat, then the slurry is covered by another sheet of moving paper facing or fiber mat so that the aqueous gypsum slurry, which will form the gypsum core, is sandwiched between the two facing materials. To reduce the overall weight of the finished gypsum board, air in the form of bubbles or air pockets may be incorporated into the aqueous gypsum slurry, resulting in a gypsum board with a foamed or bubbled gypsum core having air spaces (also called air pockets). The gypsum slurry is then allowed to set (e.g., to form an interlocking matrix of calcium sulfate dihydrate, called set gypsum) to produce a solid article before it is cut into panels and sent to a kiln for final drying.The produced plasterboard can be further processed, as is known in the art, and subsequently stacked and prepared for shipping. There are many different types and sizes of gypsum board to meet specific construction needs, such as exterior gypsum sheathing building panels, tile backer boards, or interior drywall. For example, moisture-resistant gypsum board can be manufactured for use in applications where drywall may be exposed to water, such as in bathrooms or outdoor applications. During the installation of gypsum board in the construction industry, waste materials are generated. Gypsum board can enter the solid waste stream in several different locations. These include manufacturing plants, new construction sites, renovation activities, and when a building is demolished or deconstructed. Construction site debris can be found as large pieces that can be fairly easily removed from the other components of the debris. Methods for recovering gypsum from gypsum board are well known. Methods for producing gypsum board are known. For example, published European patent application EP 2 641 886 A2 describes a gypsum powder containing hemihydrated gypsum powders and anhydrous gypsum type II powders. Anhydrous gypsum type II is obtained by calcining dihydrated gypsum recovered from gypsum board waste. EP 2 641 886 A2 further describes that a portion of the anhydrous gypsum type II can be replaced with dihydrate. Furthermore, this dihydrate can be obtained from recycled material. Gypsum board waste powders are obtained by pulverizing board waste and sieving the pulverized product to remove the papers from the boards. EP 2 030 693 B1 also describes the recycling of gypsum products in which devices (such as sieves) are provided to separate paper waste from the rest of the gypsum product waste. The published patent cooperation application WO 2009 / 064602 A1 describes the wet milling of a dihydrate in conjunction with a specific dispersant. The ground gypsum is intended for use in cosmetics, paper, or coatings as a filler. However, WO 2009 / 064602 A1 does not address the recycling of gypsum product waste. The application published under the Patent Cooperation Treaty WO 2019 / 001677 Al (Knauf GIPS KG) describes a method for producing a gypsum slurry for forming gypsum products, in particular gypsum boards, preferably gypsum paper boards, comprising the steps of: a) providing a gypsum paper product comprising a gypsum and a paper component, in particular a gypsum paper board, and / or broken parts thereof; b) wet-grinding the gypsum paper product and / or broken parts thereof containing at least parts of the paper component to form a wet-ground gypsum paper component. Its method disintegrates (grinds) the gypsum paper product together with the paper component (i.e. without prior removal of the paper component). It also includes (directly) feeding the preferably ground (uncalcined) material into a gypsum slurry to form (new) gypsum products. In another method for recovering gypsum from gypsum board, after separating the gypsum core, the board is typically ground to a particle size of about 300 pm or less (e.g., D50 of about 10 pm to 200 pm, e.g., 10 pm to 60 pm), then calcined to dehydrate the calcium sulfate dihydrate to calcium sulfate hemihydrate. This calcium sulfate hemihydrate can then be reused in a new product. US Patent No. 10,570,062 describes a method for producing a plasterboard in which powder is obtained from the stacker and added to the gypsum slurry from the plasterboard production process impregnated by the use of a hydrophobic agent, namely silicone oil. The application published under the Patent Cooperation Treaty WO 2019 / 813144 A1 describes a recycled gypsum with a foaming agent that is at least one alpha-sulfofatty acid disalt to reduce the wet density of the composition with a recycled gypsum content of at least 0.5% by weight. Japanese Patent Application Publication No. JP09165244 A describes a gypsum board material containing 3% by weight or less of a gypsum material from pulverized waste. The gypsum material from pulverized waste is ground due to the grinding power of 3-15 kW / gypsum board waste so that there is 1.04.0 m2 / g of BET specific surface area. U.S. patent application publication 2016 / 0214895 describes a method and apparatus for recycling gypsum board that includes grinding the raw material into lumps, further crushing the material in a mill that will reduce the material sizes and partially remove the backing paper from the gypsum. The material is then screened such that only the gypsum material is deposited in a hopper before entering a mixer that blends the various sizes of recycled gypsum into a consistent mixture before passing the material to a roller press subsystem to densify the material to produce material of known and uniform composition suitable for cement manufacturing. The recovered gypsum in this specific physical form factor can be used in significant portions as a replacement for virgin gypsum in cement manufacturing. The method and apparatus are applicable in the recycling of both new and refurbished gypsum-based building material. While the processes described above are relatively simple, the recovery process becomes difficult when recycling gypsum boards containing gypsum and hydrophobic materials, such as siloxanes. Attempts to recycle siloxane-containing gypsum, for example, have been unsuccessful because siloxane-containing gypsum particles interfere with the setting process of the gypsum, especially when incorporating air bubbles into the gypsum board structure. Siloxane-containing gypsum particles interfere with the incorporation of air bubbles (foaming) into the gypsum slurry. Consequently, these gypsum board products are usually not recyclable and are discarded as waste. Therefore, there is a need in the art to develop improved methods of recovering gypsum from gypsum board, in particular, to recycle gypsum materials containing hydrophobic components. BRIEF DESCRIPTION OF THE INVENTION Embodiments of the invention provide a method for making a gypsum board comprising: combining water, a first plurality of particles comprising at least about 50% by weight of calcium sulfate dihydrate and from about 0.05% by weight to about 10% by weight of hydrophobic material and having a particle size distribution with a D50 particle size of from about 200 pm to about 800 pm, as determined by Method B of ASTM D6913-17, and a second plurality of particles comprising calcium sulfate hemihydrate and optionally one or more additives to make an aqueous gypsum slurry; depositing a core layer comprising the aqueous gypsum slurry onto a molding surface; and allowing the core layer to set, thereby forming a set gypsum core. Embodiments of the invention typically comprise: combining a first plurality of particles comprising at least about 50% by weight of calcium sulfate dihydrate and from about 0.05% by weight to about 10% by weight of hydrophobic material and having a D50 particle size of from about 200 pm to about 800 pm with a second plurality of particles comprising calcium sulfate hemihydrate to form a blended calcium sulfate mixture; adding water to the combined calcium sulfate mixture to make an aqueous gypsum slurry; depositing a core layer comprising the aqueous gypsum slurry onto a molding surface; and allowing the core layer to set, thereby forming a set gypsum core. Gypsum board is a gypsum product that is plate-shaped (i.e., at least substantially flat). Gypsum board is typically rectangular in shape. BRIEF DESCRIPTION OF THE FIGURES The following figures are included to illustrate certain aspects of this disclosure and should not be viewed as exclusive embodiments. The described subject matter is susceptible to considerable modifications, alterations, combinations, and equivalents in form and function, as will occur to one skilled in the art and with the benefit of this disclosure. FIG. 1 provides a process by which gypsum material from waste can be processed to a D50 particle size of about 200 pm to 800 pm for use as reclaimed gypsum. FIG. 2 provides a process by which plaster products can be manufactured from reclaimed gypsum. FIG. 3 shows a diagrammatic side view of an example of a wet end of a continuous manufacturing line for producing gypsum board of embodiments of the invention having a gypsum core between sheets of glass mat facing. FIG. 4 shows the average NP (nail extraction) under various test conditions. DETAILED DESCRIPTION OF THE INVENTION The present invention encompasses methods that can be used to recycle gypsum materials from waste, such as gypsum board. Gypsum board from waste may comprise hydrophobic materials, such as those used in applications to improve the moisture resistance of gypsum board. In the present description, plasterboard, used in the construction of interior walls and ceilings (interior gypsum board), will be exemplified as a non-limiting example of the gypsum material from waste and the product to be made from recycled gypsum. Plasterboard, for the purposes of this description, is defined as a panel (also known as a board) comprising a core of calcium sulfate dihydrate, usually with additives, usually between sheets of front and back facing sheets. Typically, the facing sheets are made of paper or fiberglass mats, but facing sheets of other fiber sheets may be used.However, the processes described herein may be used to process and recover gypsum from any gypsum board having a core layer of gypsum-containing material and to produce a building product from any gypsum board having a core layer of gypsum-containing material. One skilled in the art would be able to modify the methods described herein to process scrap gypsum materials from interior gypsum board having a gypsum core between paper sheathing sheets, exterior sheathing gypsum board, tile backer gypsum board, or other gypsum building panels. For example, a typical gypsum exterior sheathing panel for processing in accordance with the invention may comprise, from front to back, a first fiber mat, a gypsum core layer having front and back surfaces, wherein the gypsum core layer has a thickness of about 0.64 cm (0.25 inches) to about 3.18 cm (1.25 inches), preferably about 0.64 cm (0.25 inches) to about 2.54 cm (1 inch), wherein the first fiber mat is bonded as a facing cover sheet to the front surface of the gypsum core layer, where a second fiber mat is bonded as a support cover sheet to the rear surface of the gypsum core layer. The gypsum core layer comprises greater than about 50% by weight of calcium sulfate dihydrate, preferably at least about 75% by weight more preferably at least about 85% by weight. The first fiber mat and the second fiber mat may comprise paper or fiber material (e.g., one or more of polymer fibers, glass fibers, and mineral fibers). Gypsum materials from waste can be obtained from a variety of sources. Non-limiting examples include waste from a manufacturing plant, waste from new construction sites, renovation waste, and waste from building demolition or deconstruction. In general, gypsum materials from waste comprise gypsum-containing material, typically a layer or core, and one or more facing sheets. Gypsum materials from waste comprising calcium sulfate dihydrate include gypsum boards, for example, interior plasterboard, exterior cladding panels, and tile backer boards.Likewise, waste materials comprising gypsum include specialty gypsum board products that may comprise fiberglass-reinforced gypsum cores or may be externally coated with fiberglass to strengthen the board and improve moisture resistance. The waste material comprising calcium sulfate dihydrate may also comprise components such as woven or nonwoven fiber layers comprising paper, glass fibers, mineral fibers, polymers, or the like. In particular, the gypsum board generally has a gypsum core and front and back facing sheets of paper, nonwoven fiber mat, or fiber mat. The fibers of the fiber mat or nonwoven fiber mat are typically glass fibers, mineral fibers, or polymer fibers, most commonly glass fibers.Generally, the core layer of gypsum material from waste has more than 50% gypsum by weight. In one aspect, the present invention includes a process for converting waste gypsum materials comprising a hydrophobic additive into gypsum suitable for reuse in new gypsum building materials. The resulting new gypsum building material comprises 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 waste gypsum materials. The method may comprise providing a raw waste gypsum material comprising pieces of gypsum board or other waste gypsum materials, wherein the gypsum-containing material of the raw waste gypsum material comprises greater 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.Preferably, the amount of calcium sulfate dihydrate in the raw waste gypsum material is at least about 75% by weight, more preferably at least about 85% by weight. This raw waste gypsum material is subsequently processed to generate a first plurality of particles comprising the hydrophobic additive and the calcium sulfate dihydrate. The first plurality of particles has a D50 particle size of about 200 µm to about 800 µm. The particle sizes can be determined simply by passing the materials through sieves of suitable sizes, as is known in the art. The particle size distribution (e.g., D50) can also be determined by means known in the art.For example, a non-limiting example is described in Method B of ASTM D6913 / D6913M-17: Standard Test Methods for Particle Size Distribution (Gradation) of Soils by Sieve Analysis. The hydrophobic material additives in the waste gypsum material may be a coating on the outer surface of the gypsum core and / or may be a component within the gypsum core such that the first plurality of particles comprises up to about 10% by weight, for example from about 0.05% by weight to about 10% by weight or from about 1% by weight to about 5% by weight of the hydrophobic material. Thus, by weight, a solid layer of gypsum core in the waste gypsum material may comprise up to about 10% by weight, for example from about 0.05% by weight to about 10% by weight or from about 1% by weight to about 5% by weight of the hydrophobic material. For example, a lower limit of hydrophobic material may be about 0.05% by weight, about 0.1% by weight, about 0.5% by weight or approximately 1% by weight of the gypsum-containing material. For example, an upper limit of hydrophobic material may be about 2% by weight, about 5% by weight, about 7% by weight, or about 10% by weight of the gypsum-containing material. Typical hydrophobic materials are siloxanes or waxes. Therefore, the hydrophobic additive in the waste gypsum material may be, for example, a siloxane-containing component. Hydrophobic materials tend to repel water, do not mix with water, and / or have limited wettability with water. This is the opposite of a hydrophilic material, which tends to mix with, dissolve, and / or wet with water. In another aspect, embodiments of the present invention include a process for using reclaimed gypsum comprising a hydrophobic additive to manufacture gypsum board. The method may comprise: combining water, a first plurality of particles comprising at least about 50% by weight of calcium sulfate dihydrate and from about 0.05% by weight to about 10% by weight of hydrophobic material and having a particle size distribution with a D50 particle size of from about 200 pm to about 800 pm, and a second plurality of particles comprising calcium sulfate hemihydrate to make an aqueous gypsum slurry; depositing a core layer comprising the aqueous gypsum slurry onto a molding surface; and allowing the core layer to set, thereby forming a set gypsum core. Typically, the first plurality of particles comprising calcium sulfate dihydrate (uncalcined reclaimed gypsum) is from about 0.1 wt. % to about 20 wt. %, more typically from about 1 wt. % to about 10 wt. %, also 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 with the water to form the aqueous gypsum slurry. For example, the first plurality of particles may 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 and the second plurality of particles.As used herein, "total dry weight" or "dry weight basis" refers to the weight of a mixture excluding any water that may be present. The "water component" excludes the water that may be present in a gypsum crystalline structure. In contrast, a "wet basis" includes water in the % by weight calculation. The recovered uncalcined gypsum and the second plurality of particles may be introduced into a slurry mixer as separate streams to be mixed with water and form the aqueous gypsum slurry. Alternatively, the recovered uncalcined gypsum and the second plurality of particles may be combined to form a combined gypsum stream, and the combined gypsum stream is subsequently introduced into a slurry mixer as separate streams to be mixed with water and form the aqueous gypsum slurry. In either case, the aqueous gypsum slurry may be molded into new gypsum materials suitable for use as construction materials. For example, new gypsum panels of various widths and thicknesses may be manufactured by methods known in the art.Water, and optionally one or more additives, is introduced to make the aqueous gypsum slurry either separately or with one or more of the first plurality of particles and the second plurality of particles. Preferably, the method comprises combining a first plurality of particles comprising the hydrophobic additive and calcium sulfate dihydrate, wherein the first plurality of particles has a D50 particle size of about 200 pm to about 800 pm, (herein "first plurality of particles") with a second plurality of particles comprising calcium sulfate hemihydrate to form a blended gypsum mixture. It should be noted that the first plurality of particles are not calcined prior to combining with the second plurality of particles to form the combined gypsum mixture. Therefore, as used herein, “uncalcined reclaimed gypsum” refers to this first plurality of particles comprising calcium sulfate dihydrate and the hydrophobic additive. The second plurality of particles comprising calcium sulfate dihydrate may have a D50 particle size common in gypsum board manufacturing (e.g., about 10 µm to about 100 µm) and may be obtained from mined raw gypsum, synthetic gypsum (e.g., material from flue gas desulfurization waste), or may be reclaimed and calcined. Embodiments of the invention may comprise using a foaming agent. In some embodiments, the foaming agent does not include alpha-sulfofatty acid disalts. FIG. 1 illustrates a method by which gypsum material can be processed from waste. The gypsum waste can be unused / unusable gypsum board products, scrap, or broken portions thereof. The broken portions can be accidentally and / or intentionally broken portions of gypsum products, in particular gypsum boards or (larger) broken portions thereof. The gypsum waste can comprise a gypsum layer of the gypsum material and may or may not contain at least one facing sheet, wherein the gypsum layer comprises at least about 50% by weight of calcium sulfate dihydrate and from about 0.05% by weight to about 10% by weight of hydrophobic material. In general, suitable gypsum waste, which can be recovered according to the processes described herein, has a total organic content equal to or less than about 6.4% by weight with a total paper fiber content not exceeding approximately 5.5% by weight. As obtained, a supply of plaster waste, such as plasterboard and / or broken parts thereof, can be obtained as coarse plaster, or processed into coarse plaster, namely large chunks and coarse pieces, and can therefore be processed more easily by crushing larger pieces to obtain smaller fragments. The crushing can be carried out by methods known in the art, for example, the incoming material can be reduced in size by a shredder; crusher; bucket crusher; grapple excavator or simply by passing over it with a loader. Optionally, material that does not constitute plasterboard (e.g., nails and / or other waste) can be separated at 104 to ensure that these materials do not pass to the next processing step.Subsequently, the coarse plaster fragments 106 may be introduced into a grinding step 112 to break the coarse plaster fragments 106 into gypsum particles 116. These coarse fragments 106 may be, for example, smaller than about 25.4 cm (10 inches), typically smaller than about 12.7 cm (5 inches), preferably smaller than about 5.08 cm (2 inches) in a crushing step 104. For example, the gypsum waste 106 may be crushed to obtain a raw material having a size of less than about 12.7 cm (5 inches), for example, from 1.27 to 12.7 cm (0.5 to 5 inches) or from about 1.27 cm to 5.08 cm (0.5 inches to 2 inches). The gypsum waste 102 typically has a front and / or back facing sheet. The typical facing sheet is a paper facing sheet or a woven or nonwoven fiber mat facing sheet, e.g., woven or nonwoven glass mat. The crushing 104 may cause some of the facing material (e.g., paper, glass mat) to separate from coarse gypsum fragments (e.g., the gypsum core of a gypsum board). However, some or all of the separated facing material 114 is usually removed as a separate facing sheet with a suitable cutting and grinding machine in the grinding step 112, such as a separator with a paddle screw conveyor contained in a grinding screen, which removes the facing sheet for disposal or reuse and grinds the remaining gypsum into gypsum particles 116. The grinding stage 112 may be operated under conditions sufficient to strip off the facing sheets and give the majority of the gypsum particles 116 exiting the grinding stage 112 a D50 particle size of from about 200 pm to about 800 pm, preferably from about 300 pm to about 500 pm, for example about 400 pm. Any grinding equipment may be used and one skilled in the art will be able to vary the experimental parameters of the mechanical sizing equipment to determine the appropriate speed, force, and time to generate gypsum particles 116 having the desired particle size. For example, the aforementioned separator may be used with a paddle screw conveyor contained within a grinding screen. The grinder 112 may be equipped with one or more screens 113 that allow particles of the desired size to pass through (e.g.,, from 200 pm to 800 pm) through the sieves 113 and are transported to a collection tank 118 as a plurality of recovered gypsum particles 116 having a particle size D50 of about 200 pm to about 800 pm. The recovered gypsum 116 may then be conveyed to a drywall manufacturing assembly line, such as that shown in FIG. 2. FIG. 2 depicts an illustrative sheet assembly line 200 having a first hopper 206 for receiving the recovered uncalcined gypsum 116 from the process depicted in FIG. 1. A second hopper 202 may contain calcium sulfate hemihydrate, obtained either from raw gypsum (“virgin gypsum”) or as recovered gypsum that has been calcined. The recovered gypsum 116, calcium sulfate hemihydrate (dehydrated virgin gypsum or calcined recovered gypsum) 203, along with any desired dry additives 204, may be conveyed through a chute 208 to a mixer 212. Introduction of each component into the chute 208 may be facilitated by a feed meter (not shown).Optionally and alternatively, calcium sulfate hemihydrate 203 may be introduced directly into mixer 212 through a second conduit (not shown in FIG. 2), separate from the conduit 208 that transports the recovered gypsum 116 to the mixer. One skilled in the art would be able to readily envision and employ this alternative manufacturing design. Water 210 and any desired wettable additives may be added to mixer 212 to produce an aqueous gypsum slurry. Independently, a molding table 218 may supply a continuous molding surface 216 (e.g., paper, woven fiber, or nonwoven fiber suitable as a front or back face sheet) beneath a discharge port 214 of mixer 212. The discharge port 214 deposits and spreads the gypsum slurry 220 onto the molding surface 216. The gypsum slurry 220, when set, will become the gypsum core of the gypsum board. Air or foam may be added to the gypsum slurry 220 by injecting air or foam through a conduit 232 into the aqueous gypsum slurry passing through the discharge port 214 (e.g., at the gate as described, for example, in U.S. Pat. Nos. 5,683,635 and 6,494,609). After the discharge port 214, a layer of continuous facing sheet 222 (e.g., paper, woven fiber, or nonwoven fiber suitable as a front or back facing sheet) is placed over the gypsum slurry 220 to create a layered preform assembly 225. The layered preform assembly 225 is cut to a desired length with a cutting tool 224 (e.g., a knife) into preformed panels 226. The preformed panels 226 may subsequently be passed through an oven 228 to dry the aqueous gypsum slurry and set the preformed gypsum panels 226, which emerge as fully set gypsum panels 230. A fully set gypsum panel will comprise, as a front surface, the molding surface 216, a gypsum core layer formed from the gypsum slurry 220, and a rear surface formed from the backing layer 222. It is common in the manufacture of cementitious building panels, such as gypsum wallboard, for a gypsum core layer to further comprise one or more thin, dense layers of gypsum slurry, referred to herein as a "render coat." Thus, a relatively denser layer of gypsum slurry, which will form a render coat, may be deposited on a molding surface 316 (FIG. 3) before a gypsum slurry, which is relatively less dense than the slurry used to make the render coat, is deposited and will form the bulk of the gypsum core (herein as the "main gypsum slurry"). FIG. 3 , where all like numerals represent the same elements illustrated in FIG. 2 , illustrates process 300. A portion of the gypsum slurry discharged from mixer 212 may be diverted through one or more pressurized slurry lines 303, 305 and exit through a smaller outlet port to form a first plaster coat slurry 315 on molding surface 316. If desired, additives may be wet injected into the one or more pressurized slurry lines 303, 305 through injection ports. The one or more pressurized slurry lines 303, 305 are preferably long enough to allow uniform mixing of slurry and additives. The molding surface 316 may be paper or may be a non-woven fiberglass cover sheet, for example, as used in a tile backer panel or a layered siding panel.The main gypsum slurry 320 which, when set, will form the majority of the gypsum board core may be applied on top of the first skim coat gypsum slurry 315 through the discharge port 214. As described above with respect to FIG. 2, the main plaster slurry 320 may be foamed by injecting foam or air through a conduit 232. Optionally, a second render coat gypsum slurry 317 may be deposited on top of the main plaster slurry 320. A backing (facing) material 222, e.g., paper or a second layer of nonwoven fiberglass cover sheet material, may be applied to the second render coat gypsum slurry 317 (or to the core gypsum slurry if a second render coat is not desired) and passed through a molding station to compress the layers to a desired total thickness (e.g., about 0.64 cm (0.25 inches) to about 3.81 cm (1.5 inches) thick, preferably from about 0.64 cm (0.25 inches) to about 2.54 cm (1.0 inches) thick. The resulting structure is a 325 gypsum board preform. If the main plaster slurry 320 for the core layer is foamed, the first and second plaster layer slurries 315, 317 may not be foamed, or foamed to a lesser extent, so that they are relatively denser and thinner than the foamed main plaster slurry. Therefore, the slurry MA / a / ZUZZ / UI Z / ül aqueous plaster slurry for the first and second plaster coat slurries may or may not be subject to air or foam which may be added to the main plaster slurry 320. The main plaster slurry 320 may be foamed by injecting air or foam through the conduit 232 into the aqueous plaster slurry passing through the discharge port 214. When foamed, the portion of the plaster core that is the result of the foamed and set main plaster slurry may have a total air bubble volume of from about 30 vol. % to about 90 vol. %, preferably an air bubble volume of from about 45 vol. % to about 80 vol. %. The first plaster coat and the second plaster coat (if present) that are the result of the setting of the first and second plaster coat plaster slurries may have a total air bubble volume of from about 30 vol. % or less, preferably from about 10 vol. % or less. The air bubbles in the plaster core may have an average cross-sectional diameter of less than 1.5 mm, preferably from about 0.5 to about 0.8 mm, more preferably about 0.3 mm. Typically, the first and second plaster coat slurries 315, 317 have the same composition and density. However, if desired, the first and second plaster coat slurries 315 , 317 may have different compositions and / or densities. FIG. 3 shows all of the gypsum slurries 320 , 315 , 317 coming from the same mixer 212. However, each gypsum slurry 320 , 315 , 317 may come from different mixers to have different properties, such as different densities. The calcium sulfate particles in each gypsum slurry 320, 315, 317, when combined with water, can react with the water and set as the gypsum panel preform 325 moves along a manufacturing line. The gypsum panel preform 325 can be dried and cut into segments 326 of predetermined dimensions at a time along the line where the panel preform 325 for the gypsum panel has set sufficiently. The segments 326 can be tumbled, dried 228 (e.g., in an oven) to remove excess water, and processed to provide the final layered gypsum board 330 with the desired dimensions. The combined thickness of gypsum core (including optional render layers) resulting from the set gypsum grouts 320, 315, 317 may generally be from about 0.64 cm (0.25 inches) to about 3.81 cm (1.5 inches).The combined density may be from about 240 kg / m3 (15 lb / cu ft) to about 1041 kg / m3 (65 lb / cu ft), more usually from 400 kg / m3 (25 lb / cu ft) to about 1041 kg / m3 (65 lb / cu ft), for example from 400 kg / m3 (25 lb / cu ft) to 881 kg / m3 (55 lb / cu ft). The gypsum material can be processed in the same manner described above, avoiding all calcination and thus reducing the total energy required to recycle the gypsum. Advantageously, the methods described herein allow the recovery of gypsum materials that would otherwise be unsuitable for reuse in new products. In particular, the gypsum particles, even after being reduced in size, may still contain and be coated with one or more of the hydrophobic additives present in the solid layer from which the particles were formed, which up to this point in this document are incompatible for incorporation into an aqueous gypsum slurry for the manufacture of plasterboard, particularly in plasterboard comprising foam components. Previous attempts reveal that gypsum particles with hydrophobic content rupture the walls of air bubbles, resulting in a loss of stability of the slurry.It is surprising to discover that the use of a larger particle size than that typically used in gypsum recycling, namely a D50 particle size of about 200 pm to about 1000 pm, preferably about 200 pm to about. IVIA / a / ZUZZ / UIZ / OI 800 pm, mitigates much of the incompatibility. Furthermore, these particles do not require calcination. Therefore, it was discovered that uncalcined recovered gypsum can be incorporated into an aqueous gypsum slurry at a negligible percentage (e.g., up to approximately 10% by weight or even more), thus effectively recycling what was previously unusable gypsum waste. In particular, gypsum board comprising hydrophobic components, which would otherwise be discarded, can be recycled as new gypsum board with properties conforming to ASTM C1396 / C1396M-17. Various properties, such as flexural strength, hardness (core, end, and edge), nail pullout resistance, wet deflection, end squareness, nominal thickness, depth of tapered or coved edge, width, length, water resistance of core-treated hydrophobic gypsum board products, and surface water resistance of gypsum board products with hydrophobic surfaces, can be determined as described in ASTM C473-19. All documents described herein are incorporated herein by reference for the purposes of all jurisdictions where the practice is permitted, including any priority documents and / or discovery procedures to the extent they are not inconsistent with this text. As is evident from the above general description and the MA / a / ¿U¿¿ / U1 ¿ / OI specific embodiments, although forms of the disclosure have been illustrated and described, various modifications may be made without departing from the spirit and scope of the disclosure. Accordingly, the disclosure is not intended to be limited thereby. For example, the compositions described herein may be free of any component or composition not expressly mentioned or described herein. Any method may be free of any step not mentioned or described herein. Likewise, the term "comprising" is considered synonymous with the term "including."Whenever a method, composition, element or group of elements is preceded by the transitional expression "comprising", it is understood that the same composition or group of elements is also intended to be preceded by the transitional expressions "consisting essentially of", "consisting of", "selected from the group consisting of" or "is" before mentioning the composition, element or elements and vice versa. Unless otherwise indicated, all numbers expressing quantities of ingredients, properties such as molecular weight, reaction conditions, etc., used in the present description and in the associated claims should be understood to be modified in all cases by the term "approximately". Accordingly, unless otherwise indicated, the numerical parameters set forth in the following description and in the appended claims are approximations that may vary depending on the desired properties sought to be obtained with the embodiments of the present invention. At a minimum, and not as an attempt to limit the application of the doctrine of equivalents to the scope according to the claim, each numerical parameter should at least be interpreted taking into account the number of significant digits recorded and applying customary rounding techniques. Whenever a numerical range is described with a lower limit and an upper limit, any number and any included interval that falls within the range are specifically described. In particular, each range of values ​​(in the form, "from about a to about b" or, equivalently, "from about a to b" or, equivalently, "from about a to b") described herein is to be understood to establish each number and interval comprised within the broadest range of values. Likewise, the terms in the claims have their ordinary and ordinary meaning unless explicitly and clearly defined otherwise by the patentee. In addition, the indefinite articles "a" or "an," as used in the claims, are herein defined to mean one or more of the elements they introduce. As used in this description, “NP” refers to nail extraction force. “MT” refers to products containing siloxane. “GM” means gypsum obtained from gypsum waste having a gypsum core comprising siloxane and coated with glass fiber. More particularly, the “GM” type gypsum particles described in the non-limiting examples of this disclosure had the following particle size distribution characteristics: about 15.2% by weight of the particles exceeded 840 pm, about 52.2% by weight of the particles had a size between 300 pm and 840 pm, about 19.0% by weight of the particles had a size between 150 pm and 300 pm, and about 12.0% by weight of the particles did not reach 150 pm. These particles had a D50 particle size in the range of about 200 pm to about 800 pm. One or more illustrative embodiments are presented herein. Not all features of a physical implementation are described or shown in this application for the purpose of clarity. It is understood that, in developing a physical embodiment of the present disclosure, numerous implementation-specific decisions must be made to achieve the developer's goals, such as compliance with system-related, industry-related, government-related, and other restrictions that vary by implementation and time. While a developer's efforts may be time-consuming, the efforts would nonetheless be a routine task for one skilled in the art and with the benefit of this disclosure. To facilitate a better understanding of the embodiments of the present invention, the following examples of preferred or representative embodiments are provided. The following examples should not be construed in any way as limiting or defining the scope of the invention. CLAUSES OF THE INVENTION The following clauses describe various aspects of the invention. Clause 1. A method of making a gypsum board comprising: combining water, a first plurality of particles comprising at least about 50% by weight of calcium sulfate dihydrate and from about 0.05% by weight to about 10% by weight of hydrophobic material and having a D50 particle size of from about 200 pm to about 800 pm, and a second plurality of particles comprising calcium sulfate hemihydrate to make an aqueous gypsum slurry; depositing a core layer comprising the aqueous gypsum slurry onto a molding surface; and allowing the core layer to set, thereby forming a set gypsum core. Clause 2. The method of clause 1, wherein the first plurality of particles is combined with the second plurality of particles to form a calcium sulfate blended mixture, and water is added to the calcium sulfate blended mixture to make the aqueous gypsum slurry. Clause 3. The method of clause 1, wherein the first plurality of particles is combined with the second plurality of particles to form a dry calcium sulfate blended mixture, and water is added to the dry calcium sulfate blended mixture to make the aqueous gypsum slurry. Clause 4. The method of any one of clauses 1 to 3, wherein the hydrophobic material comprises siloxane. Clause 5. The method of any one of clauses 1 to 3, wherein the hydrophobic material comprises wax. Clause 6. The method of any one of clauses 1 to 3, wherein the hydrophobic material comprises one or more of siloxane, wax and resin. Clause 7. The method of any preceding clause, wherein the first plurality of particles has a D50 particle size of about 300 pm to about 500 pm. Clause 8. The method of any preceding clause, further comprising subjecting a gypsum scrap (typically a gypsum board and / or broken portions thereof) comprising a gypsum feed material, wherein the gypsum feed material comprises at least about 50% by weight of calcium sulfate dihydrate and from about 0.05% by weight to about 10% by weight of hydrophobic material, to a size reduction process to generate the first plurality of particles. Clause 9. The method of clause 8, wherein the size reduction process comprises crushing the gypsum waste to form fragments having a dimension of 25.4 cm (10 inches) or less, preferably 12.7 cm (5 inches) or less, and grinding the fragments to generate the first plurality of particles. Clause 10. The method of any preceding clause, wherein the gypsum supply material comprises a gypsum layer and at least one facing sheet, wherein the gypsum layer comprises at least about 50% by weight of calcium sulfate dihydrate and from about 0.05% by weight to about 10% by weight of hydrophobic material, wherein the gypsum supply material comprises gypsum board comprising at least one facing sheet. Clause 11. The method of clause 10, wherein the at least one liner sheet comprises at least one of a glass mat liner sheet or a paper liner sheet. Clause 12. The method of clause 11, wherein the size reduction process at least partially removes, or completely removes, the at least one facing sheet from the plaster layer. Clause 13. The method of clause 11, wherein the size reduction process comprises crushing the gypsum waste to form fragments having a dimension of 25. 4 cm (10 inches) or less, preferably 12.7 cm (5 inches) or less, and grinding the fragments to a D50 particle size of about 200 pm to about 800 pm, preferably about 300 pm to about 500 pm, and removing the at least one facing layer from the gypsum layer. Clause 14. The method of any preceding clause, wherein the set gypsum core comprises air bubbles. Clause 15. The method of any preceding clause, wherein the set gypsum core comprises air bubbles, wherein the air 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. Clause 16. The method of any of the preceding clauses, wherein depositing the core layer onto the molding surface comprises: depositing a first portion of the aqueous gypsum slurry onto the molding surface as a plaster coat; and depositing a second portion of the aqueous gypsum slurry onto the plaster coat as a main plaster coat; and allowing the plaster coat and the main plaster coat to dry, thereby forming a set plaster core. Clause 17. The method of any preceding clause, wherein the aqueous gypsum slurry comprises from about 0.1% by weight 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. Clause 18. The method of any preceding clause, wherein the hydrophobic material comprises siloxane and wherein the first plurality of particles comprises from about 0.05% by weight to about 5% by weight, typically from 0.1% by weight to about 3% by weight, of the siloxane. Clause 19. The method of any preceding clause, wherein the hydrophobic material comprises wax and wherein the first plurality of particles comprises from about 0.5% by weight to about 10% by weight, typically from about 1% by weight to about 7% by weight, for example, from about 3% by weight to about 7% by weight of the wax. Clause 20. The method of any preceding clause, wherein the aqueous gypsum slurry comprises from about 1% by weight 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. Clause 21. The method of any preceding clause, wherein the aqueous gypsum slurry comprises from about 2% by weight to about 7% 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. Clause 22. The method of any preceding clause, wherein the aqueous gypsum slurry comprises from about 2% by weight to about 5% 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. Clause 23. The method of any preceding clause, further comprising adding air to the aqueous gypsum slurry before depositing it. Clause 24. The method of any preceding clause, wherein the set gypsum core has a total air volume of from about 30 vol. % to about 90 vol. % Clause 25. The method of Clause 24, wherein the total air volume of the set gypsum core is from about 45 vol. % to about 80 vol. % Clause 26. The method of any preceding clause, wherein the set plaster layer has a total air volume of approximately 30% by vol. or less. Clause 27. The method of any preceding clause, wherein the set plaster layer has a total void volume of approximately 10 vol. % or less. Clause 28. The method of any preceding clause, wherein at least about 98% by weight of the first plurality of particles has a particle size of about 100 pm to about 3000 pm. Clause 29. A method of making a plasterboard comprising: combining water, a first plurality of particles comprising at least about 50% by weight of calcium sulfate dihydrate and from about 0.05% by weight to about 10% by weight of hydrophobic material and at least about 98% by weight of the first plurality of particles having a particle size of from about 100 pm to about 3000 pm, and a second plurality of particles comprising calcium sulfate hemihydrate to make an aqueous gypsum slurry; depositing a core layer comprising the aqueous gypsum slurry onto a molding surface; and allowing the core layer to set, thereby forming a set gypsum core. Clause 30. The method of clause 29, wherein the first plurality of particles is combined with the second plurality of particles to form a blended calcium sulfate mixture, and water is added to the blended calcium sulfate mixture to make the aqueous gypsum slurry. Clause 31. The method of clause 30, wherein the first plurality of particles is combined with the second plurality of particles to form a dry calcium sulfate blended mixture, and water is added to the dry calcium sulfate blended mixture to make the aqueous gypsum slurry. Clause 32. The method of any of clauses 29 to 32, wherein the hydrophobic material comprises one or more of siloxane, wax and resin. Clause 33. The method of any one of clauses 29 to 32, wherein the aqueous gypsum slurry comprises from about 0.1% by weight to about 20% by weight of the first plurality of particles based on a combined dry weight of the first plurality of particles and the second plurality of particles. Clause 34. The method of any of the clauses 9 to 32, wherein the aqueous gypsum slurry comprises from about 1% by weight to about 10% by weight of the first plurality of particles based on a combined dry weight of the first plurality of particles and the second plurality of particles. Clause 35. The method of any one of clauses 29 to 34, wherein the hydrophobic material comprises siloxane and wherein the first plurality of particles comprises from about 0.05% by weight to about 5% by weight, typically from 0.1% by weight to about 3% by weight, of the siloxane. Clause 36. The method of any one of clauses 29 to 34, wherein the hydrophobic material comprises wax and wherein the first plurality of particles comprises from about 0.5% by weight to about 10% by weight, typically from about 1% by weight to about 7% by weight, for example, from about 3% by weight to about 7% by weight of the wax. EXAMPLES Table 1 below describes the manufacture of four different gypsum board products using various quantities of uncalcined reclaimed gypsum containing siloxane. Two types of waste products were processed to obtain uncalcined reclaimed gypsum. "MT" type gypsum was obtained from gypsum waste having a gypsum core comprising siloxane and coated with paper. More particularly, the "MT" type gypsum particles had the following particle size distribution characteristics: about 23.6% by weight of the particles exceeded 840 pm, about 41.1% by weight of the particles had a size between 300 pm and 840 pm, about 20.0% by weight of the particles had a size between 150 pm and 300 pm, and about 14.2% by weight of the particles did not reach 150 pm. A minimal amount (e.g., about 1.5% by weight or less) of paper and / or glass fiber may also be mixed with the plurality of recovered gypsum. These particles had a D50 particle size in the range of about 200 pm to about 800 pm. Type "GM" gypsum was obtained from gypsum waste having a gypsum core comprising siloxane and coated with glass fiber. More particularly, the "GM" type gypsum particles had the following particle size distribution characteristics: about 15.2% by weight of the particles exceeded 840 pm, about 52.2% by weight of the particles had a size between 300 pm and 840 pm, about 19.0% by weight of the particles had a size between 150 pm and 300 pm, and about 12.0% by weight of the particles did not reach 150 pm. These particles had a D50 particle size in the range of about 200 pm to about 800 pm. Manufactured Product “A” is 5 / 8 inch (1.59 cm) fire-resistant, paper-faced, fiberglass-reinforced Type X gypsum board. Product “B” is 5 / 8 inch (1.59 cm) fire-resistant, moisture- and mold-resistant paper-faced, fiberglass-reinforced Type X gypsum board. Product “C” is 1 / 2 inch (1.27 cm) lightweight gypsum panel. Product “D” is 1 inch (2.54 cm) fire-resistant, fiberglass-reinforced Type X gypsum board, fiberglass-faced. Table 1 Product E.g. Uncalcined “MT” type Uncalcined “GM” type Nail extraction results (Ibf) Comments A 1 0 0 107.7 control A 2 0.7 1.3 110.7 performed similarly or better at nail extraction than control A 3 0.7 2.2 113.4 B 4 0 0 108.1 control B 5 0.7 1.3 114.3 performed similarly or better at nail extraction than control B 6 0.7 2.2 111.9 C 7 0 0 77.2 control c 8 0 2 78.8 performed similarly or better in nail extraction than the control c 9 0 3.4 81.4 D 10 0 0 na control D 11 0 0.8 na No effect The above products “A”, “B”, “C” and “D” were successfully prepared with the properties described in Table 2 below. Table 2 Product Thickness (inches) Density (lbs / ft3) A 0.625 43.7 B 0.625 43.6 C 0.495 33.7 D 1 50.5 Previously, attempts to use hydrophobic-containing gypsum particles were unsuccessful due to the antifoaming properties of the hydrophobic-containing gypsum particles causing the gypsum slurry, 220 in FIG. 2 and 320 in FIG. 3, to collapse and preventing the formation of a preformed gypsum core 225 in FIGs. 2 and 3, resulting in the plasterboard manufacturing process stopping. A collapsed gypsum core has a volume 6 total voids (or air bubbles) less than about 30%. During the manufacture of these examples, no foam reduction or obvious gypsum core collapse was observed in the manufacture of product boards of types "A", "B", "C", and "D" when the reclaimed gypsum particles having a particle size in the range of 200 µm to 800 µm were used. In some cases, increasing the total soap which increased the strength of the air bubble walls effectively counteracted any antifoaming action of the hydrophobic-containing gypsum particles and prevented gypsum core collapse, thereby allowing continued operation of the plasterboard manufacturing process. After drying, the properties of the resulting boards in the various tests described above showed no visible defects compared to the controls (i.e., Examples η.os1, 4, 7, and 10). Boards made from uncalcined reclaimed gypsum had essentially the same properties, such as nail extraction, as boards made from calcined materials, as shown in Table 1. FIG. 4 shows the nail pullout strength of boards made in accordance with the invention. 1 / 2 inch thick gypsum boards (comprising a core and a top and bottom cover sheet) were prepared with various amounts of uncalcined scrap. The figure shows that the nail pullout strength is not statistically different from the control. The control contains 0% of the first plurality and has a weight of 1360 lbs per 1000 sq ft (6640 kg / m2) of the 1 / 2 inch board. Therefore, the present description is adapted to achieve the purposes and advantages mentioned, as well as those inherent therein. The foregoing particular description is merely illustrative, as the present description may be modified and practiced in different, but equivalent, ways obvious to one skilled in the art and with the benefit of the teachings herein. Furthermore, it is not intended to limit the construction or design data shown herein beyond what is described in the claims below. It is noted that in relation to this date, the best method known to the applicant to put the aforementioned invention into practice is the one that is clear from the present description of the invention.

Claims

1. A method for preparing a gypsum board, characterized in that it comprises: combining water, a first plurality of particles comprising at least approximately 50% by weight of calcium sulfate dihydrate and from approximately 0.05% by weight to approximately 10% by weight of hydrophobic material, wherein the first plurality of particles has a D50 particle size of approximately 200 pm to approximately 800 pm and a second plurality of particles comprising calcium sulfate hemihydrate to prepare an aqueous gypsum slurry; depositing a core layer comprising the aqueous gypsum slurry onto a molding surface; and allowing the core layer to set, thereby forming a set gypsum core.

2. The method according to claim 1, characterized in that the first plurality of particles is 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 make the aqueous gypsum slurry.

3. The method according to claim 1, characterized in that the first plurality of particles is combined with the second plurality of particles to form a combined dry calcium sulfate mixture and water is added to the combined dry calcium sulfate mixture to make the aqueous gypsum slurry.

4. The method according to claim 1, characterized in that the hydrophobic material comprises one or more siloxane, wax, and resin.

5. The method according to claim 1, characterized in that the first plurality of particles has a particle size D50 of approximately 300 pm to approximately 500 pm.

6. The method according to claim 1, characterized in that it further comprises subjecting a gypsum waste comprising a gypsum supply material to a size reduction process to generate the first plurality of particles, wherein the gypsum supply material comprises A) at least approximately 50% by weight of calcium sulfate dihydrate and B) hydrophobic material, wherein the gypsum supply material comprises a gypsum layer and optionally at least one facing sheet, wherein the gypsum layer comprises at least approximately 50% by weight of calcium sulfate dihydrate and from approximately 0.05% by weight to approximately 10% by weight of hydrophobic material, wherein the gypsum supply material comprises gypsum board comprising at least one facing sheet.

7. The method according to claim 6, characterized in that the at least one lining sheet comprises at least one glass mat lining sheet and one paper lining sheet, wherein the size reduction process at least partially removes the at least one lining sheet from the gypsum layer.

8. The method according to claim 1, characterized in that the aqueous gypsum slurry comprises from approximately 0.1% by weight to approximately 20% by weight of the first plurality of particles based on a combined dry weight of the first plurality of particles and the second plurality of particles.

9. The method according to claim 1, characterized in that the aqueous gypsum slurry comprises from approximately 1% by weight to approximately 10% by weight of the first plurality of particles depending on a combined dry weight of the first plurality of particles and the second plurality of particles.

10. A method for preparing a gypsum board, characterized in that it comprises: combining water, a first plurality of particles comprising at least approximately 50% by weight of calcium sulfate dihydrate and from approximately 0.05% by weight to approximately 10% by weight of hydrophobic material, and at least approximately 98% by weight of the first plurality of particles having a particle size of approximately 100 µm to approximately 3000 µm, and a second plurality of particles comprising calcium sulfate hemihydrate to prepare an aqueous gypsum slurry; depositing a core layer comprising the aqueous gypsum slurry onto a molding surface; and allowing the core layer to set, thereby forming a set gypsum core.