Expandable polymeric materials and useful articles incorporating same - Patents.com

Abstract

The present invention provides absorbent materials comprising a hydrogel-forming swellable polymer and a plasticizer, which exhibit advantageous performance characteristics, such as advantageous fluid absorption capacity, fluid absorption rate and rewetting, which are within at least about 80% of similar characteristics exhibited by crosslinked polyacrylate superabsorbent polymers, or the cumulative performance of the advantageous performance characteristics is equal to or better than that exhibited by crosslinked polyacrylate superabsorbent polymers. The present invention also relates to articles of manufacture comprising such absorbent materials and methods of manufacture.

Description

[Technical field]

[0001] Related Applications This application claims the benefit of U.S. Provisional Application No. 63 / 245,129, filed September 16, 2021, the entire contents of which are incorporated herein by reference.

[0002] Field of application FIELD OF THE DISCLOSURE This application relates to expandable polymeric materials and articles formed therefrom. [Background technology]

[0003] background Superabsorbent polymers, which will be described in more detail below, are specialized crosslinked polymer networks that are characterized by their ability to absorb many times their weight in liquid while remaining intact in the presence of the absorbed liquid.Their absorbent and retaining properties can make them useful in any setting where fluid needs to be absorbed and retained in a convenient form factor.Thus, superabsorbent polymers (SAPs) form the basis of many consumer products that rely on their ability to absorb aqueous fluids, such as baby diapers, adult incontinence pads, feminine care products, etc.

[0004] In common use, SAP is derived primarily from acrylic acid, a polymer synthetically formed from acrylate monomers, which themselves are derived from petrochemical sources and are considered a non-renewable resource dependent on the petroleum industry. Furthermore, the process required to form SAP from acrylate monomers consumes significant energy, entails expenses, and imposes an environmental burden. Currently, SAP is estimated to constitute about 27% of the weight of conventional baby diapers, and their manufacture contributes about 34.5% of the Global Warming Potential (CO2eq) impact for diaper production. The high contribution of CO2 emissions from SAP production and processing highlights the environmental impact of conventional SAP.

[0005] The manufacturing process for SAP hydrogels can result in residual acrylate monomers that become embedded in the final product. Residual monomers in SAP can leach out of the absorbent polymeric material into the surrounding aqueous fluids that come into contact with human tissue and enter the environment. Although techniques have been devised to minimize the levels of residual monomers in SAP, the presence of these substances, even in small amounts, can cause skin irritation and health problems and can pollute the environment.

[0006] The most significant environmental hazard posed by traditional SAPs is their resistance to biodegradation. Scientific studies have shown the slow rate of SAP degradation under normal environmental conditions. A study investigating the biodegradability of polyacrylate polymers used as soil conditioners found that the predominantly long chains of polyacrylate polymers in hydrogels degraded "at a rate of 0.12-0.24% per 6 months, if at all." (Biodegradability of a polyacrylate superabsorbent in agricultural soil Burkhard Wilske & Mo Bai & Beate Lindenstruth & Martin Bach & Zahra Rezaie & Hans-Georg Frede & Lutz Breuer, Environ Sci Pollut Res DOI 10.1007 / s11356-013-2103-1). Studies have shown that for higher molecular weight SAPs, the rate of biodegradation can be even slower.

[0007] Personal care items, including SAPs, such as baby diapers and adult incontinence products, are disposed of in municipal solid waste. According to an EPA report, in 2018, 3.3 million tons of disposable personal care items were consigned to landfills; this tonnage was equivalent to approximately 1.4% of the total municipal solid waste in the United States for that year. It is estimated that discarded disposable diapers take approximately 450 years to decompose.

[0008] Despite the limitations of traditional SAP as an absorbent material, such as health and stability concerns and sustainability concerns, the SAP has been widely adopted. One report indicates that 90-95% of American infants use diapers with SAP, and approximately 27.4 billion single-use diapers are used annually. Disposable diapers incorporate performance features that result in extended dryness and reduced leakage. However, considering the burden that these products are placed on the environment, there is a need in the field to improve the products to be more sustainable while retaining their beneficial characteristics. Alternatives to traditional SAP derived from natural sources have been proposed, but these alternatives tend not to provide the same high performance as traditional SAP.

[0009] Thus, alternatives to traditional polyacrylate SAPs advantageously come from natural sources and impose less stress on the environment while providing similar performance to consumers.Desirably, natural and biodegradable superabsorbent polymers can provide an alternative to SAP absorbency and can be easily incorporated into existing manufacturing processes for absorbent articles, thus avoiding capital expenditures and simplifying the path to commercialization.Such materials can be used as absorbents in other applications, for example, in pet waste management; biodegradable superabsorbent polymers advantageously provide a more sustainable alternative to clay minerals or silica gels, which are envisioned to be used as pet waste absorbents, for example, in animal litter. Summary of the Invention

[0010] overview In an embodiment, an absorbent material is disclosed herein, which comprises at least one hydrogel-forming swellable polymer, for example at least one bio-based hydrogel-forming swellable polymer; and a plasticizer; wherein the absorbent material exhibits advantageous performance properties selected from the group consisting of fluid absorption capacity, fluid absorption rate and rewetting, or the advantageous performance properties are within at least about 80% of the similar properties exhibited by conventional superabsorbent polymers, or the cumulative performance of the advantageous performance properties is equal to or better than the performance exhibited by conventional superabsorbent polymers. In an embodiment, the absorbent material is biodegradable or compostable. In an embodiment, the at least one polymer is a biodegradable synthetic polymer or bio-based, and in an embodiment, the at least one polymer exhibits superabsorbent properties. In an embodiment, the at least one polymer is an anionic polymer, which may be alginate or carrageenan. In an embodiment, the at least one polymer is a cationic polymer or a neutral polymer. In embodiments, the polymer is a polysaccharide, which may be selected from the group consisting of dextrin, dextran, agarose, cellulose, and derivatives of any of the foregoing. In embodiments, at least one polymer is a polysaccharide selected from the group consisting of xanthan gum, alginic acid, and sodium alginate. In embodiments, the plasticizer is selected from the group consisting of small molecules, polymeric polyols, and oligomers. In embodiments, the absorbent material includes a second plasticizer. In embodiments, at least one of the plasticizer and the second plasticizer is a small molecule, and the small molecule is a polyol, which may be glycerol, glycerin, maltitol, or xylitol. In embodiments, the plasticizer is an oligomer, which may be a glucose oligomer or a cellulose oligomer. In embodiments, the absorbent material further includes one or more additional bio-based hydrogel-forming expandable polymers. In embodiments, the absorbent material includes a crosslinker, which may be a covalent or ionic crosslinker, or a secondary crosslinker, such as a divalent cation found in bodily fluids. The absorbent material may be crosslinked internally, on its surface, or both.The absorbent material may further comprise a catalyst for the cross-linking agent. In an embodiment, the absorbent material further comprises a plasticizer additive or a functional additive. In an embodiment, a method for forming a solid biodegradable absorbent material of a pre-specified shape is also disclosed herein, wherein the solid biodegradable absorbent material exhibits advantageous performance characteristics selected from the group consisting of fluid absorption capacity, fluid absorption rate and rewetting, or the advantageous performance characteristics are within at least about 80% of the similar characteristics exhibited by conventional superabsorbent polymers, or the cumulative performance of the advantageous performance characteristics is equal to or better than the performance exhibited by conventional superabsorbent polymers, and the method includes the steps of: preparing a liquid composition comprising at least one bio-based hydrogel-forming swelling polymer, a plasticizer and a surfactant; processing the liquid composition in a shape-forming device, wherein the shape-forming device is selected from the group consisting of an extruder, a die, an electrospinner, a slot die and a fluid dispenser, and the shape-forming device forms the liquid formulation into a selected three-dimensional form that corresponds to the pre-specified shape; and fixing the selected three-dimensional form, thereby producing the pre-specified shape.In an embodiment, the solid biodegradable absorbent material is a semi-solid material. In an embodiment, the at least one bio-based hydrogel-forming polymer is a polysaccharide, the plasticizer is glycerol or xylitol, and the surfactant is capryl glucoside or hexyl glucoside. In an embodiment, the pre-specified shape is an elongated chain or a flattened sheet or a flat shape or an oval shape. In an embodiment, the shape-forming device is an extruder, which may have a devolatilization capability to evaporate excess water. In an embodiment, the solidification step includes a sub-step of drying the selected three-dimensional form to form the pre-specified shape. In an embodiment, the polymer is biodegradable or compostable. In an embodiment, the method further includes a step of adding a cross-linking agent to the hydrogel mixture before the orienting step.In an embodiment, the method further comprises the step of adding an additive having advantageous properties to the hydrogel mixture prior to the directing step, where the additive can be a filler additive, which can be selected from the group consisting of fluff pulp, microfibrillated cellulose and nanofibrillated cellulose. In an embodiment, the additive is an odor absorbing additive. In an embodiment, the additive has specialized properties. In an embodiment, the method further comprises the step of heating the formed absorbent material after the directing step.

[0011] Also disclosed are articles of manufacture comprising a disposable absorbent region, wherein the disposable absorbent region comprises an absorbent material as described herein, the disposable absorbent region being organized as a multi-layer structure. In an embodiment, the multi-layer structure comprises one or more layers of absorbent material, the absorbent material being a foam material. In an embodiment, the multi-layer structure comprises at least one primary absorbent layer formed from an absorbent material, and at least one secondary absorbent layer. In an embodiment, the at least one primary absorbent layer may be formed as a sheet, which may be perforated by one or more apertures. In an embodiment, the at least one primary absorbent layer comprises portions of absorbent material that overlap each other, creating gaps that allow fluid to pass through the layers. In an embodiment, the at least one secondary absorbent layer comprises a paper-based material. In an embodiment, the at least one secondary absorbent layer is sandwiched between a first primary absorbent layer and a second primary absorbent layer. In an embodiment, the disposable absorbent region further comprises at least one of a specialized inner layer and a specialized outer layer. The specialized outer layer may include a biopolymer with barrier properties. The specialized inner layer may include a functional additive. In an embodiment, the article of manufacture further includes a reusable outer shell that positions the disposable absorbent region proximate to an anatomically advantageous region within the article of manufacture. In an embodiment, the article of manufacture is selected from the group consisting of diapers, incontinence pads, feminine hygiene products, pet litter, and pet training pads. The article may be a personal care product, which may be selected from the group consisting of diapers, adult incontinence products, fluid absorbent pads, and feminine hygiene products. The article may be intended for medical use, which may be selected from the group consisting of wound treatment, blood clotting, treatment of skin conditions, surface application of medical or health treatments, and transdermal application of medicinal treatments. [Brief description of the drawings]

[0012] BRIEF DESCRIPTION OF THE DRAWINGS [Figure 1] FIG. 1 shows a schematic cross-sectional view of a layered absorbent region. [Figure 2-1] FIG. 2A shows a schematic cross-sectional view of a multi-layer absorbent region. [Figure 2-2]2B and 2C each show a schematic top view of a multi-layer absorbent region, such as that shown in FIG. 2A. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Detailed Description 1. Absorbent materials made from renewable resources In an embodiment, disclosed herein is an absorbent material comprising a bio-based hydrogel formed from renewable resources. Such materials are understood to be naturally derived, biodegradable and environmentally sustainable. The term "sustainable" has many meanings in current usage, generally referring to being able to maintain a set of conditions or behaviors at a certain rate or level over a period of time; when used in the environmental context, the term generally refers to avoiding the depletion of natural resources and maintaining ecological balance. Advantageously, the materials described herein are intended to contribute to this desired goal of sustainability, which is defined by the EPA as "creating and maintaining the conditions under which humans and nature can exist in productive harmony, which allows the social, economic and other requirements of present and future generations to be met" (Executive Order 13514 (2009) Federal Leadership in Environmental, Energy, and Economic Performance).

[0014] The absorbent material disclosed herein contributes to sustainability because it is naturally derived and biodegradable, in contrast to absorbent materials derived from non-renewable sources, such as petroleum (i.e., conventional superabsorbent polymers or SAPs).As used herein, "conventional superabsorbent polymers" are polyacrylate superabsorbent polymers, such as crosslinked polyacrylate superabsorbent polymers.In embodiments, the absorbent material disclosed herein can be used in personal and pet care products, such as baby diapers, adult incontinence pads, feminine hygiene products, and animal litter.In embodiments, articles comprising the absorbent material disclosed herein exhibit advantageous performance characteristics, such as fluid absorption capacity and fluid absorption rate (wicking rate), and rewetting, where one or more of these performance characteristics are within commercially acceptable ranges. For example, one or more of these performance characteristics may be within about 80% of the same or similar characteristics exhibited by articles containing conventional superabsorbent polymers, or may be within about 85% of the same or similar characteristics, or may be within about 90% of the same or similar characteristics. In another example, one or more of the advantageous performance characteristics exhibited in articles containing absorbent materials disclosed herein are within about 80% of the same characteristics, or within about 85% of the same characteristics, or within about 90% of the same characteristics exhibited by articles containing conventional superabsorbent polymers, for example, the fluid absorption capacity and fluid absorption rate (wicking rate), and / or rewetting of the adsorbent material of the present invention may be within about 80%, 85% or 90% of the fluid absorption capacity and fluid absorption rate (wicking rate), and / or rewetting, respectively, of the adsorbent material containing conventional superabsorbent polymers. In embodiments, the cumulative performance of all performance characteristics is within a commercially acceptable range, but no isolated performance characteristic is within at least about 80% of the similar characteristic, or within at least about 85% of the similar characteristic, or within at least about 90% of the similar characteristic exhibited by articles containing conventional superabsorbent polymers. In embodiments, commercially acceptable ranges of performance characteristics are understood by those of skill in the art.In aspects, the cumulative performance of the advantageous performance characteristics for articles comprising the absorbent materials disclosed herein is equal to or better than those performance characteristics exhibited by articles comprising conventional superabsorbent polymers.

[0015] More specifically, the hydrogels disclosed herein are formed from polymers that exhibit superabsorbent properties, the term "superabsorbent" referring to the ability of a material to absorb at least 10 times its dry weight of aqueous liquid. The term "polymer" refers to a macromolecule having a degree of polymerization of at least 1000. In embodiments, the polymer may have a molecular weight of at least 1000 Daltons. The polymer may be a homopolymer, copolymer, terpolymer, or other polymer grouping recognized as such by those skilled in the art; the polymer may be linear, branched, and / or crosslinked. Superabsorbent polymers, such as those disclosed herein, are understood when crosslinked to absorb fluids via osmosis and form a relatively durable gel, which may be referred to as a "hydrogel".

[0016] Advantageously, the superabsorbent polymers (or SAPs) disclosed herein are produced in whole or in part by living organisms or derived from living organisms or other renewable resources. For the purposes of this disclosure, renewable resources are natural products that are replenished, restored or regenerated within a fairly short time frame, e.g., less than 100 years. In contrast, natural resources, such as petroleum, coal, minerals from the earth and peat, take more than 100 years to replenish themselves and therefore are not included as renewable resources. Renewable resources can be replenished naturally or through agricultural or other engineering techniques. Agricultural techniques include farming the land and farming animals, fish or other living organisms (bacteria, algae, fungi, etc.). By way of example and without limitation, renewable resources include plants, animals, fish, bacteria, fungi, and forestry products or by-products, any of which may be naturally occurring, hybridized, or genetically engineered, any of which may be obtained from their primary natural environment or from an engineered environment, such as culture or hydroponic horticulture. Materials derived from such renewable resources may also be referred to as "bio-based" materials.

[0017] Advantageously, the bio-based SAP materials disclosed herein are biodegradable and compostable. Biodegradation is mineralization (i.e., the breakdown of a material into its mineral components, which may simply be carbon dioxide and water, or may include other minerals, such as nitrates, sulfates, halogens, etc., depending on the composition of the material itself), which results from the action of microorganisms, such as bacteria and fungi, on the material. Materials that can be broken down by biodegradation may be referred to as "biodegradable", as that term is used herein. In contrast, many synthetic materials, such as petroleum-derived plastics, are resistant to biodegradation, understood to be limited in part by their molecular weight, chemical structure, and water solubility. Importantly, these synthetic materials are xenobiotics, i.e., those that were not present in the environment until recently, and they were not included in the evolutionary process that formed the metabolic pathways in microorganisms that can cause their degradation. In contrast, naturally occurring bio-based polymers are found in or derived from living organisms, and therefore have evolved in symbiosis with microorganisms that can break them down. Thus, biodegradation of bio-based polymers occurs relatively quickly, especially for bio-based polymers that have hydrolyzable bonds in their backbones, such as cellulose, hemicellulose, and various polysaccharides.

[0018] Biodegradation begins with the encounter of microorganisms with biobased materials, which then secrete various extracellular enzymes that depolymerize the biobased materials. Once the polymers are reduced to a size that renders the fragments water soluble, these fragments can be absorbed by microorganisms and subjected to microbial metabolic pathways that mineralize the fragments. Other chemical processes not attributable to the activity of living organisms, such as chemical decomposition and photooxidation, can occur before or during these microbially driven processes as part of the biodegradation process. The term "compostable" is often used interchangeably with biodegradation, although several more specific legal definitions exist to distinguish this term from biodegradation. For example, the European standard EN13432 defines minimum standards for a packaging material to be considered compostable: 1) disintegration (i.e., fragmentation and loss of visibility in the final compost, where at least 90% of the composted material can pass through a 2x2mm sieve), where the residue from the original material is <10% of the original mass after 3 months; 2) biodegradability, where 90% of the composted material is converted to CO2 by microbial action within 6 months; 3) absence of negative effects of the composting process; 4) less than certain amounts of heavy metals and fluorine.

[0019] 2. Absorbent materials, including bio-based hydrogels In an embodiment, the absorbent material disclosed herein comprises a bio-based hydrophilic and water-swellable polymer that forms a hydrogel. As used herein, the term "bio-based" refers to a material that can be obtained from a renewable resource derived from a living organism, such as a material formed by a plant, a microorganism, or an animal. As used herein, the term "natural" also refers to such a material. A hydrogel is understood to be a three-dimensional network of hydrophilic polymers that can swell in water and hold a relatively large amount of water while maintaining a three-dimensional structure due to chemical or physical interactions of the component polymer chains. As used herein, the term "hydrogel" refers to a relatively water-insoluble gel that is formed by containing water within a matrix of a water-swellable material. A hydrocolloid is a colloidal system in which hydrophilic polymers are dispersed in water; hydrocolloids, whether sol or gel, can be in different states depending on the component materials and the amount of water available. Hydrocolloids can also alternate between sol and gel states, for example, when exposed to initial or other physical or chemical agents.

[0020] Certain hydrogels may be formed of crosslinked or entangled networks of linear homopolymers, linear copolymers, or block or graft copolymers. Other hydrogels may be formed as interpenetrating networks, physical mixtures, or hydrophilic networks stabilized by hydrophobic domains. In other examples, hydrogels may be formed as polyion-polyvalent ion complexes or polyion-polyion complexes or hydrogen-bonded complexes. Hydrogels may be reversible (physical) or permanent (chemical) hydrogels. Physical hydrogels include: simple entanglement systems, where water-containing polymeric networks are held together by molecular entanglements or crystallites; ion-mediated networks, where the network is stabilized by interactions between oppositely charged polyelectrolytes and polyvalent ions; and thermally induced networks, which form three-dimensional structures in response to heating or cooling. Chemical hydrogels include linked structures, such as crosslinked polymers or copolymers, or polymerized interpenetrating networks, supported primarily by covalent bonds. Hydrogels can also be formed by crosslinking or entanglement that occurs in response to external stimuli such as the application of light and temperature changes. Light stimuli are particularly advantageous for crosslinking applications because their delivery is easy to control and quantitate. Light can be switched on and off, and the dose can be precisely controlled to achieve the desired functional effect. Furthermore, the light wavelength can be specifically selected to produce the desired properties in the resulting hydrogel. Although ultraviolet light exposure is advantageous, other wavelengths can be selected where appropriate.

[0021] Materials used to form bio-based hydrogels include natural hydrophilic polymers that absorb significant amounts of water or aqueous fluids (including, but not limited to, body fluids) in a relatively short period of time. In other words, such polymers are water-swellable. Water-swellable polymers can be dispersed in a liquid phase, such as water, where they can absorb such water; when crosslinked, water-swellable polymers in an aqueous environment can form a hydrophilic polymer network that ensnare the liquid within the network through surface tension effects and hydrogen bonding, thus forming a gel. Crosslinked water-swellable polymers, such as those disclosed herein, can soak up, complex with, or otherwise bind to water, forming a three-dimensional network known as a hydrogel. The hydrophilic groups on the polymer can account for the strong hydrophilicity of the water-swellable polymer network. Water-swellable polymer networks can range from moderately absorbent, typically holding 10-30 wt.% water within their structures, to superabsorbent, where they hold several times their weight in aqueous fluid. When water-swellable polymer networks are formed into stable three-dimensional gel structures, the structures are referred to as hydrogels, as described above. In embodiments, hydrogels contain at least 10% water.

[0022] Water-swellable polymers and the hydrogels formed therefrom can be themselves or derived from natural materials. For example, natural water-swellable polymers include anionic polymers such as alginates and carrageenans, and cationic polymers such as chitosan, and neutral polymers. In embodiments, water-swellable polymeric materials can include naturally derived hydrocolloids, which include high molecular weight hydrophilic polymers whose polar or charged functional groups make them soluble in water and further impart water-swellable properties. Naturally derived water-swellable polymers include polysaccharide polymers such as dextran, dextrin, agarose, cellulose, starch, and their derivatives. Polysaccharides have the added advantage of biodegradability and tolerance in line with well-recognized regulations for personal care and other health and wellness applications. More specifically, suitable hydrogels and hydrocolloids for forming bio-based absorbent materials may include, but are not limited to, xanthan gum, pectin, amylopectin, carrageenan (or including, but not limited to, kappa, iota, or lambda carrageenan), alginates and alginates (including, but not limited to, derivatives such as propylene glycol alginate), agar-agar, cellulose gum, cellulose (such as, but not limited to, carboxyalkylcelluloses, such as, but not limited to, carboxymethylcellulose, hydroxyethylcellulose, carboxymethylhydroxyethylcellulose, etc.), pectin esters, gums such as gellan gum, guar gum and guar derivatives, gum arabic, locust bean gum, diutan, welan, tarn, frankincense, karaya, ghatti, damar, tragacanth, or modifications or mixtures of any of the foregoing. In embodiments, polysaccharides, such as those described herein, are particularly advantageous for their swelling properties in the case of high molecular weight or high viscosity formulations.For example, polysaccharides having molecular weights up to about 90,000 daltons, up to about 100,000 daltons, up to about 150,000 daltons, or higher molecular weights up to about 1,000,000 daltons, or molecular weights from about 50,000 to about 2,000,000 daltons are useful for forming hydrogels. In certain embodiments, lower molecular weight polymers are useful, such as cellulose ether polymers having a molecular weight in the range of about 10,000 to about 100,000 daltons, e.g., about 10,000 daltons.

[0023] Mixtures of hydrogels derived from nature can also be formed. For example, polysaccharides such as starch, modified starch, amylose, modified amylose, cellulose such as cellulose ethers and cellulose esters, chitosan, modified chitosan, chitin, modified chitin, gelatin, konjac, modified konjac, fenugreek gum, modified fenugreek gum, mesquite gum, modified mesquite gum, aloemannan, modified aloemannan, oxidized polysaccharides, sulfated polysaccharides, cationic polysaccharides, etc. can be used alone or in combination with other such materials in any ratio. In embodiments, mixtures of cellulose ether polymers can be prepared for use as absorbent materials. For example, formulations containing hydroxyethylcellulose and hydroxypropylmethylcellulose can be prepared, optionally combined with plasticizers such as glycerol and surfactants (e.g., capryl glucoside, hexyl glucoside, etc.) to form absorbent polymers. The high or low molecular weight ratio components of the formulation can be adjusted to provide advantageous properties. In embodiments, formulations can be prepared that contain about 0.5% to about 5% or about 0.5% to about 4% or about 1% to about 2% naturally derived hydrogel, and can include surfactants and plasticizers in ratios of hydrogel portion to surfactant of about 1:1.5 ratio of hydrogel:surfactant to about 2:1 ratio of hydrogel:surfactant, for example, 1:1 ratio of hydrogel:surfactant, and ratios of hydrogel portion to plasticizer of about 95:5 ratio of hydrogel:surfactant to about 99:1 ratio of hydrogel:surfactant. In preferred embodiments, the hydrogel comprises about 1.2% of the formulation, the ratio of hydrogel:surfactant is about 1.5:1, and the ratio of hydrogel:glycerol is about 95:5.

[0024] Polysaccharide polymers are advantageous for forming absorbent materials. As an example, xanthan gum (XG) can be used. XG is an anionic polysaccharide that is resistant to wide variations in temperature, pH, and salinity. XG can form robust helical structures due to the availability of hydrogen bonds between its trisaccharide side chains and its polymer backbone. As a result, the random spatial orientation of these robust helices gives them the ability to be highly swellable when crosslinked. As another example, alginic acid polymer or sodium alginate can be used. Alginic acid is a linear copolymer in which homopolymeric blocks of (1→4)-linked β-D-mannuronate (M) and α-L-guluronate (G) residues are each covalently bonded together in a different sequence or block. The monomers can be found in consecutive G-residues (G-blocks), homopolymeric blocks of consecutive M-residues (M-blocks), or alternating M and G-residues (MG-blocks). Note that α-L-guluronate is the C-5 epimer of β-D-mannuronate. In embodiments, biodegradable synthetic polymers may also be used, such as polyvinyl alcohol, polyvinyl acetate, polylactic acid, polyglycolic acid, polylactic-co-glycolic acid, and the like, or mixtures thereof. Polysaccharide polymers capable of absorbing at least 50, at least 100, at least 300, at least 500, at least 800, at least 900, or at least 1000 times their weight in water are particularly useful.

[0025] High molecular weight expandable polymers may be particularly advantageous for expansion due to their ability to produce highly entangled porous networks, and in embodiments may be preferred to smaller molecular weight molecules. In other embodiments, creating highly entangled networks from smaller molecular weight polymers (or creating "ultra" high molecular weight polymer networks from already high molecular weight polymers) may greatly increase expansion capabilities. Polymer mixtures may be used to create this ultra-high molecular weight network by charge-charge complex formation. In embodiments, highly branched and charged expandable polymers may be used and mixed with oppositely charged polymers. The branched components may then be combined to form a stable network. In embodiments, plasticizers (as described in more detail below), such as glycerin, may be used to promote absorption and maintain the apertures, pores or other channels between the two oppositely charged polymers to support openness. As used herein, the term glycerol refers to the pure form of the glycerol molecule (1,2,3-propanetriol), and glycerin refers to a preparation that contains about 95% glycerol.Plasticizers such as glycerin exert their beneficial effects due to the presence of glycerol in glycerin; it is understood that using pure glycerol as a plasticizer is similarly advantageous.

[0026] Small amounts of any neutrally charged plasticizer, oligomer or polymer may also be used between the polymer complexes to prevent excessive aggregation or precipitation. It is envisioned that the network thus formed may be sufficiently stable that no cross-linking or minimal cross-linking may be required.

[0027] In embodiments, a positively charged polymer may be used as the majority component, and a negatively charged polymer may be used sparingly and provide binding. These may be varied, with the negatively charged polymer providing swelling and the positively charged polymer creating binding. Various amounts may be used, such as ratios of swelling polymer to binding polymer of 90:10 to 95:5. In embodiments, the major polymer component is highly swelling, and in other embodiments, both component polymers are highly swelling. In embodiments, cationic starch may be used in combination with a polymer of the opposite charge, such as CMC, alginate, pectin, etc.

[0028] In embodiments, mixtures of more linear polymers can be prepared to produce a single high molecular weight entangled polymer that has a different polymer configuration than a polymer containing linked branched components. In embodiments, a small amount of a positively charged polymer, such as chitosan, can be used with a larger amount of a cost-effective negatively charged polymer, such as CMC, alginate, pectin, etc. A plasticizer, such as glycerin, can be used to lubricate the chains, support their opening, allow for more water uptake, and prevent clumping or precipitation. The polymer charge can be varied, but various amounts can be used, such as ratios of 90:10 to 95:5. In embodiments, the main polymer component is highly swellable, and in other embodiments, both component polymers are highly swellable.

[0029] In embodiments, other additives may be included in the water-swellable polymer formulation (whether such formulation contains only a single hydrogel-forming polymer or a mixture of such polymers) to improve performance characteristics such as fluid absorption (capacity), fluid absorption rate (wicking rate) and rewetting. By way of example, the addition of glycerin or a similar compound to the formulation may improve certain aspects of performance such as wicking rate. In embodiments, glycerin may be added in small amounts, such as between about 0% and about 30%, or between about 0% and about 20%, or between about 5% and about 15%, or between about 5% and about 10% of the add-on polymer. In embodiments, glycerin may be added in small amounts, such as between about 0% and about 5%, or between about 10% and about 15%, or between about 15% and about 20%, or between about 20% or about 25%, or between about 25% and about 30%. As an example, glycerin can be added to an XG formulation in an amount of about 10%: a coating formulation containing 10% XG polymer and 1% glycerin can improve swelling performance and improve coating consistency with reduced flaking and increased ductility.

[0030] Water uptake in bio-based hydrogels can be increased by adding a plasticizer material. As used herein, the term "plasticizer" refers to a low volatility, low molecular weight organic material that, for example, reduces its viscosity and increases its glass transition temperature (T g Plasticizers are added to polymers to improve their physical / handling properties, such as their flexibility, flow and / or thermoplasticity, without changing their chemical nature, by changing the elasticity or modifying the modulus of the polymer composition. Without being bound by theory, plasticizers can improve the mechanical properties of a polymer system by interacting with the polymer chains and facilitating their physical interaction with each other, or by occupying the space between the polymer chains and increasing the free volume between them, allowing them to slide and rotate more freely, thereby improving the T g and reducing the melt viscosity.

[0031] Plasticizers useful for improving water uptake in bio-based hydrogels may include one or more types of low molecular weight hygroscopic materials, such as small molecules or oligomers. Examples of small molecules include polyols, such as glycerol or glycerin, ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, hexylene glycol, butylene glycol, polyethylene glycol, propylene glycol, tripropylene glycol, sorbitol, mannitol, maltitol, xylitol, erythritol, isomalt, and the like. Polymeric polyols, such as polydextrose, may also be used. As another example, suitable plasticizers may include other hygroscopic materials, such as acetin, glyceryl triacetate, urea, collagen, and the like. Oligomers may also be used as plasticizers, such as dimers, trimers, tetramers, and the like. Examples of oligomers include glucose oligomers, such as dextrose, maltose, maltotriose, maltotetraose, and the like. Cellulose oligomers may also be used, such as cellotriose, cellotetraose, and the like. Any of these plasticizer materials may be used alone or in combination with one another in any ratio, such as in an amount of about 0% to about 30%, or about 0% to about 20%, or about 5% to about 15%, or about 5% to about 10% of the included polymer. In embodiments, the plasticizer may be added in small amounts, such as in an amount of about 0% to about 5%, or about 10% to about 15%, or about 15% to about 20%, or about 20% to about 25%, or about 25% to about 30%. The plasticizer additive may increase the rate, amount, and retention of the bio-based hydrogel matrix, such as allowing for more rapid uptake of bodily fluids, such as urine, a greater ability to retain a volume of bodily fluids, and / or retention of bodily fluids for a longer period of time within the hydrogel matrix.In embodiments, plasticized biobased hydrogels can be formed from highly viscous solutions of a selected polymer or polymers, the hydrogels comprising from about 1% to about 50% of the polymer or polymers, or from about 5% to about 25% of the polymer or polymers, to which one or more plasticizers have been added in amounts, e.g., from about 0% to about 30%, or from about 0% to about 20%, or from about 5% to about 15%, or from about 5% to about 10%, of the polymer involved, or alternatively, the plasticizers have been added in other lesser amounts, e.g., from about 0% to about 5%, or from about 10% to about 15%, or from about 15% to about 20%, or from about 20% to about 25%, or from about 25% to about 30%.

[0032] After the plasticized hydrogel is formed, it can be optionally crosslinked. Crosslinking agents can be added during the manufacturing process, or crosslinking precursors can be added that are intended to form after the hydrogel is exposed to bodily fluids, such as urine. In embodiments, the hydrogel can be crosslinked on the surface, either during the manufacturing process or secondarily (e.g., upon exposure to bodily fluids). In other embodiments, the hydrogel can be partially or entirely crosslinked within the material. In still other embodiments, a combination of surface and internal crosslinking can be used.

[0033] In an embodiment, surface cross-linking can be advantageous in preventing gel blocking, which occurs when hydrogel particles, which may be used in the absorbent pad of a diaper or personal care article, pack and expand after absorbing a certain amount of liquid, and then the hydrogel particles deform, shift, and clump together, blocking voids in the support matrix of the absorbent pad and inhibiting further transmission of liquid to other parts of the absorbent pad.

[0034] However, the surface crosslinks are designed to be relatively weak and do not prevent bead expansion, but as a result, the surface crosslinks may not be strong enough to withstand the stresses of expansion or stresses associated with load bearing when the article is worn, and rewetting may occur easily. In embodiments, internal crosslinks may be advantageous in addition to or instead of surface crosslinks. Increasing internal crosslinks may increase the gel strength of the liquid-saturated absorbent particles, thereby increasing the structural integrity of the absorbent layer.

[0035] In embodiments, the crosslinks can be tailored to achieve a particular result, balancing multiple factors, such as preventing gel blocking, maintaining sufficient structural stability, and providing sufficient absorption capacity and absorption rate. In embodiments, the absorbent particles can be formed into shapes that facilitate an optimal balance of these factors. For example, in embodiments, particles with elongated or high aspect ratios can be formed to optimize absorbency, yet maintain structural stability, and interfere with gel blocking.

[0036] Crosslinking agents that can be added to the hydrogel include covalent and ionic crosslinking agents. Covalent crosslinking agents include di- and multifunctional epoxies, citric acid, butanetetracarboxylic acid, poly(methyl vinyl ether-alt-maleic anhydride), polymeric methylene diphenyl isocyanate, poly(ethylene glycol) and diglycidyl ether. Ionic crosslinking agents include salts with divalent ions, such as calcium chloride, magnesium chloride, calcium citrate, magnesium citrate, calcium acetate, magnesium acetate, and the like. Monovalent or other polyvalent salts can be used as well. Catalysts can be added to accompany certain crosslinking agents, as will be understood by those skilled in the art. Crosslinking can also occur secondarily due to exposure to bodily fluids, such as urine. It is understood that urine contains divalent cations, which act as secondary crosslinking agents that can crosslink certain anionic hydrogel polymers, such as alginates, carboxymethylcellulose, and the like.

[0037] Further examples of crosslinking agents include polyglycidyl ether compounds, haloepoxy compounds, polyaldehyde compounds, polyhydric alcohol compounds, polyamine compounds and polyisocyanate compounds. Particularly advantageous are polyglycidyl ether compounds such as polyfunctional epoxides, for example ethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, glycerol-1,3-diglycidyl ether, glycerol triglycidyl ether, triglycidyl ether of propoxylated glycerin, polyethylene glycol diglycidyl ether and 1,6-hexanediol diglycidyl ether. Examples of haloepoxy compounds include epichlorohydrin and a-methyl epichlorohydrin. Examples of polyaldehyde compounds include glutaral-dehyde and glyoxal. Examples of polyhydric alcohol compounds include glycerol, ethylene glycol, diethylene glycol, propylene glycol, polyethylene glycol, polypropylene glycol, diethanolamine and triethanolamine. Examples of polyamine compounds include ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, polyamide resins as reactants of polyamines and aliphatic polybasic acids and polyamidepolyamine epichlorohydrin resins. Examples of polyisocyanate compounds include toluene diisocyanate and hexamethylene diisocyanate.

[0038] When using epoxy crosslinkers, base, tertiary ammonia and quaternary ammonium catalysts may be added to achieve the appropriate crosslinking conversion. Depending on the source and grade of polysaccharide used, different amounts of crosslinker may be used. To achieve this, crosslinkers with flexible and extendable arms between crosslinking sites may be selected, allowing the internal polymer chains within the polysaccharide coating to expand upon absorption of liquid, allowing the matrix to retain liquid and expand.

[0039] In embodiments, the crosslinker formulation may include a multifunctional epoxy with oligomeric arms. Such bulky crosslinkers are slow to diffuse, especially in the viscous solutions used to generate absorbent particles. This highly viscous layer results in a reduced crosslinker diffusion rate, which directs the reaction preferentially to the surface of the layer, the interior of which remains unconstrained and uncrosslinked. The unconfined interior of the coating layer allows for its easy expansion / expansion. In yet other embodiments, crosslinking is not required or advantageous and may therefore be omitted.

[0040] 3. Shaping absorbent materials for use in articles of manufacture The absorbent material formed from the bio-based hydrogel formulation disclosed herein can be formed into any useful shape, including but not limited to beads, pellets, strands, fibers, chips, sheets, plates, etc. The shape of the absorbent material can be tailored for a particular application by directing the absorbent material composition described above through a suitable shape-forming device, which can form the composition into a three-dimensional form that corresponds to the final formation into a desired pre-specified useful shape. The shape-forming device can be an extruder, electrospinner, slot die, mold, or any other device available in the art for forming a liquid formulation into a solid or semi-solid structure, which has a predetermined three-dimensional form that corresponds to a pre-specified shape. As used herein, the term "liquid" refers to a material that takes the shape of the container in which it is held and is not solid; liquids include semi-fluid materials, such as gels, which are flowable but highly viscous. In contrast, a solid is a state of matter that retains its shape and density when unconfined. A semi-solid material is a non-flowable material that is not easily pourable, but is less dense and rigid than a solid. A non-flowable gel that remains in its formed shape may be considered a semi-solid. As described in more detail below, the shape-forming device may transform a liquid or semi-fluid material into a solid or semi-solid material having a preselected shape. In an embodiment, the shape-forming device itself is sufficient to form the liquid or semi-fluid material into a pre-specified shape for the solid or semi-solid material. In another embodiment, the shape-forming device forms the liquid or semi-fluid material into a three-dimensional form that can then be dried to produce a pre-specified shape for the solid biodegradable absorbent material.

[0041] The shape for the absorbent material is selected based on the commercial needs for the absorbent article: for example, flat chains or randomly shaped particles may be more useful for diaper manufacturing as opposed to round beads or chains, which may accumulate in the dependent areas of the diaper. As another example, the chains or fibers may align themselves better with other filler materials, such as wood pulp or fluff pulp, for applications such as animal litter, where softness and "foot feel" are important. In embodiments, elements with elongated forms, especially those with high aspect ratios, are less likely to contribute to gel blocks. Thus, elongated shapes may be advantageous in preventing gel blocks in absorbent articles, in addition to the cross-linking strategies previously mentioned. Multiple shapes may be engineered into the absorbent material, depending on the needs of a particular absorbent article. For example, in embodiments, the absorbent material may be formed as long flat chains with lower aspect ratios, or as flat sheets, instead of particles, cylinders, or beads. For example, a mold may form a liquid absorbent material substrate into a pre-determined three-dimensional structure.

[0042] In one version of the manufacturing process, a mixture of high viscosity hydrogel-forming polymer and plasticizer can be metered into and pumped from a drop tower, which acts as a shape former by allowing the formation of droplets from fluids forced through orifices in the drop tower head, similar to the formation of water droplets from a showerhead. As the droplets descend from the drop tower head, they solidify and assume a symmetrical shape. The shape and hardness of the droplets can be adjusted as they solidify by exposure to heat and countervailing airflow. For example, air blowers at the bottom or sides of the droplet stream can provide airflow and / or heat to retard the descent of the droplets, adjust the droplet size, accelerate gel setting, or facilitate crosslinking. In processing methods intended to increase crosslinking, the droplets can be released from the drop tower head as described above and directed into a bath containing a crosslinking solution. The resulting crosslinked droplets may be removed from the bath by filtration, centrifugation, or other methods well known in the art. The hydrogel particles produced by the techniques described above can be further cut or processed to obtain a desired size or shape.

[0043] In another version of the manufacturing process, an extruder can be used as a shape forming device. In an exemplary embodiment, a homogeneous high viscosity hydrogel mixture containing one or more selected natural polymers and one or more plasticizers is produced in a mixing tank, a crosslinker is added if necessary, and other additives are optionally included. An advantageous formulation includes a mixture of hydroxyethyl cellulose (HEC) and hydroxypropyl methylcellulose (HPMC), which is combined with a plasticizer, such as glycerol or glycerin, and a surfactant, such as capryl glucoside or hexyl glucoside; such a formulation may have a HEC:HPMC ratio ranging from about 95:5 to about 70:30, such as 80:20, or from about 95:5 to about 60:40. The absorbent polymer in the formulation is added in an amount of about 1% to 2% by weight, such as about 1.2%. The ratio of absorbent polymer to surfactant is about 1.5:1, and the ratio of absorbent polymer to glycerol is about 95:5.

[0044] To prepare an exemplary formulation, glycerol can be added to water and magnetically stirred for about 5 minutes, after which a surfactant, such as capryl glucoside or hexyl glucoside, can be added and further mixed if done with an overhead mixer. The selected polymer (e.g., CMC or HPMC) or mixture of polymers as described above can be added to the solution and mixed for a specified period of time (e.g., 5-20 minutes at 300 rpm, then the speed is reduced to 150 rpm and further mixing for 6-10 hours). Crosslinking agents can be added at any stage of the mixing process, for example, by adding non-instantaneous crosslinking agents; in embodiments, non-instantaneous crosslinking agents can rearrange ionic ones (which take effect immediately) and crosslinking can take place at any stage of the reaction, while in other embodiments, ionic crosslinking agents can be added at the end of the reaction and take effect immediately. If a catalyst is used to facilitate crosslinking, the crosslinking agent can be added at any suitable point, and the catalyst is added at the end of the reaction period.

[0045] After the ingredients are mixed, the resulting mixture is pumped through an extruder with devolatilization capabilities to evaporate excess water and produce extruded strands of material. Crosslinking agents and / or catalysts that are activated upon heating can be included in the mixture or added during the extrusion process, and the formed extruded material begins to crosslink upon passing through the extruder. Heating elements / equipment can be added after extrusion to heat the extruded material to cause sufficient crosslinking. Crosslinking and / or heating of the extruded material can solidify the extruded material, which assumes and retains a desired pre-specified shape.

[0046] In another exemplary version of the manufacturing process, the fibers or strands can be formed by electrospinning. In such a process, a homogeneous high viscosity mixture containing one or more selected natural polymers and one or more plasticizers is produced in a mixing tank, a crosslinker is added if necessary, and other additives are optionally included. A formulation useful for this purpose includes a mixture of hydroxyethyl cellulose (HEC) and hydroxypropyl methylcellulose (HPMC), which is combined with a plasticizer, such as glycerol or glycerin, and a surfactant, such as capryl glucoside or hexyl glucoside; such a formulation can have a HEC:HPMC ratio ranging from about 95:5 to about 70:30, such as 80:20, or from about 95:5 to about 60:40. The absorbent polymer in the formulation is added in an amount of about 1% to 2% by weight, such as about 1.2%. The ratio of absorbent polymer to surfactant is about 1.5:1, and the ratio of absorbent polymer to glycerol is about 95:5. A preferred formulation includes HEC and HPMC polymers at a concentration of 1.2% of the total solution, with the ratio of absorbent to glycerol being about 95:5, and the ratio of absorbent to surfactant being about 1.5:1. After the solution is mixed, it can be introduced into a conventional electrospinning machine, for example, by passing the solution through a plastic tube and flowing it into the solution reservoir for the electrospinning device. The solution is then fed from the solution reservoir to the needle point of the electrospinning machine. A high voltage is generated at the needle tip, and the solution is injected into the needle and exits the tip to reach the following collector plate. The collector plate is typically a polished aluminum plate. The potential difference between the needle tip and the collector plate causes the polymer solution to spin out of the needle tip, producing an array of fibers on the plate, with fiber dimensions ranging from nanometers to micrometers in diameter. These fibers can be arranged into randomized polymer networks that can be formed into other shapes, for example, as absorbent sheets.To prepare a final shaped product from the extruded or electrospun material for use in an article of manufacture, the hydrogel strands resulting from this process can be solidified, dried and cured to form elongated hydrogel strands, which can be cut into a desired elongated, oval, flat, or any regular or irregular bead, fiber, strand, sheet, or chip shape. The diameter of the desired beads or strands will likely be 1-3 mm for use in absorbent personal care items, or larger (e.g., 5-10 mm) for use in pet absorbent products such as animal litter. Although the above process has been described with respect to the formation of beads or elongated strands, it is understood that the final shape for the absorbent particles can be tailored to achieve a particular purpose, such as reducing the degree of gel blockage that occurs in absorbent articles such as diapers, or providing a large flat absorbent surface, as in a flat absorbent sheet.

[0047] As another example, a mixture of high viscosity hydrogel-forming polymer and plasticizer can be prepared as a sheet. A flat structure such as a sheet can be formed in a mold or by an extrusion process, in either case the liquid-absorbent material structure can enter a shape-forming device, be confined to or spread over the surface of the device, and solidify, e.g., dry, into a solid, flat, sheet-like structure. The use of a mold allows other design features to be added to the sheet, such as patterns, apertures, thickness variations, formed features, or other shape variations.

[0048] The sheets formed of absorbent material can be used individually in absorbent articles, or multiple sheets can be incorporated into the article. The sheets can be of any size or thickness, and can have areas of various thicknesses or patterned variations in thickness. The sheets can be embossed with patterns that are advantageous to a particular absorbent article, for example, to promote increased wicking and / or reduce gel blocking. The sheets can be patterned with cutouts or other void areas, for example, to promote water flow, or the sheets can be sculpted with three-dimensional channels or columns, for example, to promote wicking to other absorbent layers of the same or other materials. In embodiments, the sheets can be stacked, connected to each other, and / or wrapped, printed on, or otherwise incorporated into layers made of other materials, such as pulp or porous paper. The absorbent sheets may be used in a variety of absorbent articles, for example, for flat or shaped absorbent articles such as diapers or incontinence pads, or for pet training or "potty" pads, or between layers of pulp for animal litter, such as cat litter.

[0049] In an exemplary embodiment, a sheet can be formed by preparing a formulation, such as that described above, and mixing overnight in an overhead mixer, after which it can be spread onto a silicone mat or carbon pan and placed in an oven at 45 or 70° C. for 3-7 hours to dry. The sheet produced thereby can be rolled out to a preselected thickness with a roller before or during drying, or the sheet can be flattened to a preselected thickness before drying, recognizing that the thickness will shrink when the sheet dries. For example, a sheet that is 2 mm thick when wet can shrink to a thickness of 0.03 mm when dry. In an embodiment, a wet sheet that is about 1.5-3.5 mm thick can shrink to a thickness of about 0.2 mm-1 mm during drying. Once the sheet on the mat or pan is dry, it can be peeled off the pan and incorporated into an article of manufacture, as described in more detail below.

[0050] In certain embodiments, the absorbent material is not pre-shaped separately, but is dispensed onto the biodegradable carrier in a preselected pattern, where a dispenser for fluids (e.g., liquid dispensing equipment, such as nozzles, sprayers, extruders, slot dies, etc.) acts as a shape former. The absorbent material prepared as described above can be dispensed onto the carrier in an arrangement appropriate for the article of manufacture, and the absorbed fluid is advantageously channeled, directed, or retained. The carrier can be selected from a wide range of biodegradable materials. In embodiments, carriers derived from wood pulp can be used, such as paper-based materials or pulp-based products, such as fluff pulp. Paper-based materials of different consistencies can provide different properties to the absorbent article: certain paper-based materials (such as those formed into products such as paper towels) can be more absorbent, while others, such as those formed into face or bath tissues, provide a softer surface when the article contacts the skin. Paper-based materials can be manufactured in various thicknesses, selected to optimize their advantageous properties, such as absorption or strength, as appropriate for a particular article of manufacture. Thinner sheets of paper-based materials can be arranged in layers, and individual layers can be treated differently with absorbent materials to absorb or wick fluids in specific patterns. A particular carrier sheet can, for example, be prepared to be more hydrophobic and combined with one or more layers of other carrier sheets that are less hydrophobic. In embodiments, an interior or exterior carrier sheet, such as a sheet of paper, can be treated to have oil-, grease-, and / or water-resistant (OGWR) properties. In embodiments, such a sheet or a set of layered sheets with OGWR properties can be placed on or towards the externa aspect of a formed article, which can provide an exterior barrier to prevent migration of fluids from the article of manufacture to the environment.

[0051] The layered arrangement of carrier sheets treated with absorbent materials disclosed herein can be separated by sheets of absorbent material itself, taking advantage of the ability of the treated carrier sheets to direct the flow of fluids in combination with the ability of the absorbent material to absorb large amounts of fluid. An exemplary arrangement of layers to create an absorbent region in an article of manufacture is shown in FIG. 1. FIG. 1 shows a schematic cross-sectional view of such an absorbent region 100. As used herein, the term "absorbent region", such as the absorbent region 100 shown by FIG. 1, refers to an absorbent structure suitable for use alone as an absorbent article or that can be incorporated into a more complex article of manufacture. When incorporated into a more complex article of manufacture, the absorbent region can also be referred to as an "absorbent core", depending on the relationship of the absorbent region to other features of the article of manufacture. Exemplary applications of absorbent regions, described with respect to this figure, are provided below.

[0052] In the embodiment of the absorbent region 100 shown in FIG. 1, layers of biodegradable carrier material 102 are interleaved with layers of absorbent material 108. Although the layered arrangement appears to include spaces between the layers, such spaces are only to make the individual layers more easily visible. Spaces between the layers may be provided in the absorbent region 100, but more typically the layers are closely juxtaposed to one another. In an embodiment, the layers of carrier material 102 and absorbent material 108 are compressed together, resulting in a thinner cross section for the absorbent article 100. In the embodiment shown, the layers of carrier material 102 carry a dispersion of absorbent material 104 on their upper surfaces. Although the multiple regions of absorbent material 104 on the surface of the carrier material 102 appear as regularly spaced droplets or dots in the figures, it is understood that any pattern of distribution of absorbent material 104 may be arranged, whether regular or irregular, continuous or discontinuous, with parallel straight lines, converging or overlapping lines, serpentine, dotted, scattered, shaped as a grid or network, or otherwise, to achieve the desired purpose of the absorbent region 100. In embodiments, such absorbent material 104 distributed on the carrier material 102 is optional. In embodiments, the layer of absorbent material 108 is optional, and the carrier material 102 and one or more layers of optional absorbent material 104 disposed thereon provide the desired absorbency.

[0053] Methods for dispersing absorbent material 104 on carrier material 102 are well known in the art. For example, the biodegradable absorbent polymer solution disclosed herein can be dispensed from an applicator or sprayed onto carrier material 102 when the absorbent polymer solution is still in liquid form. In such an arrangement, optionally, the carrier material can have some hydrophobic properties, so that any fluid that strikes the layer is preferentially directed to the absorbent polymer arrangement instead of being non-specifically absorbed into the carrier material itself. In embodiments, the dispersion pattern for the absorbent polymer solution is arranged in channels to direct the fluid in a particular direction, e.g., for wicking preferentially through a portion of the absorbent region. The carrier material 102 holding the liquid absorbent polymer solution on its surface can then be dried, e.g., in an oven at 45-70° C. for 3-7 hours, which allows the carrier material layer 102 holding absorbent material 104 to be conveniently aligned with and sandwiched between other components of the absorbent region. In particular, the absorbent material 104 on the carrier material 102 may be in contact with an overlying sheet of absorbent material 108. The absorbent material 104 disposed on the carrier material 102 may be the same as or different from the absorbent material in the separate absorbent material layer 108.

[0054] While the carrier material 102 (optionally provided with a dispersion of absorbent material 104) and the layer of absorbent material 108 are shown as substantially similar in the illustrated embodiment of FIG. 1, it is understood that any of these layers may differ in size, shape, physical properties, absorbency, etc. The carrier material 102 itself may be processed separately from providing a dispersion of absorbent material 104. For example, the carrier material may be textured with a pattern to allow directional flow or wicking of liquids, and may be perforated to allow liquids to flow through. In embodiments, the carrier material 102 may include other additives within these materials, as described in more detail below. Similarly, if optional absorbent layers 108 are provided, they may be similar to each other or different from each other, consistent with the absorbency requirements of the absorbent region 100. Some layers may be thicker than others to increase absorbency. For example, the inclusion of an absorbent layer 108 that is less absorbent toward the top of the absorbent region 100 (where it is first exposed to the liquid 114) may allow liquid to pass through the top layers of the absorbent region 100 and wick away from the skin or other sensitive surfaces that come into contact with the top of the absorbent region 100. To avoid trapping liquid within the absorbent region structure itself or the carrier material 102, the layers may be otherwise engineered to allow liquid movement, for example, by providing holes, slits, or other mechanical features that enhance fluid flow. In embodiments, the absorbent region may be formed with a predominant absorbent layer 108 and fewer layers of carrier material 102.

[0055] As shown in FIG. 1, optional specialized inner and outer layers may be added to the layered arrangement described above. For example, a top layer 112 of softer material may be included as a point of contact with the skin or other sensitive surface. This top layer 112 may include functional additives having advantageous properties, as described in more detail below: for example, additives that impart softness and excellent hand feel to the product, such as plasticizers (e.g., glycerin, PEG, Pluronic, etc.), or vitamins (e.g., Vitamin E), or agents for treating diaper rash or other skin conditions, may be included in this inner layer. Desirably, the top layer 112 is permeable to the liquids 114 it encounters, so that the liquids 114 may be absorbed by the remainder of the absorbent region 100 without contacting the skin or other sensitive areas. The addition of the specialized top layer 112 and the properties of such specialized top layer 112 may be determined based on the article of manufacture within which the absorbent region 100 is to be included. For example, personal care items such as diapers may have more use for a specialized upper layer 112 that is closer to the subject's skin, as opposed to pads designed for general use, such as dog training pads or disposable medical underpads, where skin contact is not present or is not prolonged.

[0056] A bottom layer 110 may be optionally applied to the absorbent region 100 as well. In embodiments, the bottom layer may be water-resistant or waterproof and / or oil- and grease-resistant. Water, oil- and grease-resistant may be imparted by a number of techniques well known in the art, depending on the needs of the particular article of manufacture. For example, an outer waterproof layer for a personal care item may prevent any absorbed fluid from passing from the absorbent region 100 to the environment. Such a layer may also protect the absorbent region 100 from encountering fluids in the environment. Desirably, any special properties imparted to the outer layer 110 result from the use of biodegradable polymeric materials ("biopolymers"), so that the entire article of manufacture is biodegradable. As used herein, the term "biopolymer" refers to a polymer produced by a living organism during its life. Exemplary formulations may include a mixture of bio-based materials, such as methylcellulose, hydroxypropylmethylcellulose, glycerol, and the like, optionally including additives, such as nanofibrillated cellulose and microfibrillated cellulose, as described in US Patent Application 17 / 834,521, filed June 7, 2022, the entire contents of which are incorporated herein by reference. Such formulations may include some or all of the following components: methylcellulose, hydroxypropylmethylcellulose, glycerol, and microfibrillated cellulose, and may be available for processing into a water-resistant outer layer, for example, as a 5% solution in water. Such a solution may be sprayed onto a layer of carrier material 102 or incorporated into a layer of carrier material to impart water-resistant properties to such layer, which may then form the outer layer 110 of the absorbent region 100. Formulations including these components may alternatively be formed as separate sheets, which may then function as separate outer layers 110 of the absorbent region.

[0057] Examples of biopolymers with barrier properties for water resistance and / or oil-grease resistance include, but are not limited to, exopolysaccharides such as bacterial cellulose, kefiran, pullulan, levan, gellan, and other polysaccharides such as alginates, cellulose, carrageenan, gum arabic, starch, and vegetable glucomannans such as locust bean gum, mannan, guar gum, and the like. Useful biopolymers may also include biopolyesters such as polyhydroxy-alkanoates and polylactic acid derivatives. In preferred embodiments, cellulose biopolymers may be used in the formulation to provide the desired degree of oil / grease or water resistance for the outer layer 110. A range of cellulose polymers exist with various polymers having different degrees of hydrophobicity or oleophobicity, and the cellulose polymers may be selected to produce the desired degree of oil, grease, and / or water resistance for the outer layer 110. In embodiments, it may be beneficial to mix one or more cellulose polymers with other materials that are more hydrophobic to provide greater water resistance. For example, methylcellulose provides good oil / grease resistance, but not so much water resistance.Methylcellulose can be mixed with another cellulose biopolymer, such as hydroxypropyl methylcellulose, to provide greater water resistance.In an embodiment, a mixture of methylcellulose and cellulose acetate can be provided to adjust both oil / grease resistance and water resistance properties.Cellulose acetate and lipid are some examples of additives that can be used to adjust oil / grease resistance coating to be more hydrophobic, and the combination of this with more oleophobic material can provide both oil and water resistance.

[0058] In preferred embodiments, multiple layers can be used to form an absorbent region, where layers of absorbent material are separated by a secondary absorbent sheet, such as a paper-based material, sandwiched between them. An exemplary embodiment of an absorbent region 200 according to these principles is shown in FIG. 2A. Using this layered approach, the number of layers and their composition can be determined by the needs of a particular useful article, taking into consideration factors such as the expected service duty, the liquid holding capacity of the article and its constituent layers, and the desired overall thickness of the product. A multi-layer structure, such as that shown in FIG. 2A, includes at least one primary absorbent layer and at least one secondary absorbent sheet; in embodiments, multiple absorbent layers can be separated by a secondary absorbent sheet, such as where at least one secondary absorbent sheet is sandwiched between two primary absorbent layers, which can be the same or different from each other. The layer of absorbent material or secondary absorbent sheet may optionally be embossed, stamped, or otherwise patterned to increase the effective surface area and / or enhance the lateral transmission of incident fluids. In contrast to bulky conventional designs, such as debonded fluff pulp around a SAP bead core, the layered designs contemplated herein lend themselves to a thin cross-sectional profile. The layered absorbent region 200 embodiment shown in cross-section in FIG. 2A features layers of absorbent material 202a disclosed herein, which may be separated by a secondary absorbent sheet 208, taking advantage of the ability of the secondary absorbent sheet and any patterns added to these materials or their surfaces to increase the effective surface area, direct fluid flow, or both, in combination with the ability of the layer of absorbent material 202a to absorb large amounts of fluid. The secondary absorbent sheet 208 may also have selected absorbent properties to improve the overall absorbency of the absorbent region 200. In embodiments, the secondary absorbent sheet 208 may be formed of materials that are the same or different in composition than the absorbent material 202 forming the thicker layer.In preferred embodiments, the secondary absorbent sheet 208 is formed of a material different from the absorbent material 202a, e.g., a paper-based material, as described for use as a carrier material, e.g., as described with respect to FIG. 1. In certain preferred embodiments, the secondary absorbent sheet comprises or consists of a paper-based material, such as a highly wicking low-density, highly porous paper, e.g., that used for filter paper, paper towels, tissue paper, and the like. Paper is a particularly advantageous material for layering above and below layers of absorbent material: the paper is made of randomly stacked pulp fibers with voids between them, so that it acts as a co-continuous matrix, as described in more detail below. Desirably, a highly wicking low-density, highly porous paper-based material, e.g., filter paper, paper towels, tissue paper, and the like, is used rather than a coated paper or a high-density sheet (e.g., office paper). The layered arrangements disclosed herein are consistent with a wide range of design choices and process latitudes. For example, the top and bottom gel layers may have different porosity than the layers between them, and the exterior layers (top and bottom) may have different compositions and textures.

[0059] As shown in FIG. 2A, a layer of absorbent material 202a (i.e., the primary absorbent layer) is provided with apertures, e.g., holes, holes, channels, or other voids 204a, that allow some of the fluid 214 that encounters the layer to pass through it with minimal absorption. In other embodiments, the apertures, e.g., holes, holes, channels, or other voids, can be designed to facilitate fluid flow in a particular direction, e.g., toward the center of the absorbent region, or to improve the overall absorbency of the layer. For example, certain holes extend transmurally to allow fluid flow-through passage, while other holes extend only partially into the layer and act as fluid receptacles that facilitate fluid absorption within such layer. Channels can also extend from the periphery to the center, concentrating fluid in a more absorbent central region, or extend from the center to the periphery or otherwise, distributing the deposit of fluid more evenly across the absorbent layer. Although the layer of absorbent material 202a is shown to have a uniform thickness, it is understood that it can have any desired thickness and any type of thickness variation. For example, the primary layer of absorbent material 202a can be thicker in the middle of the absorbent region to improve absorption in such regions, if a larger volume of fluid is placed there, or the primary layer of absorbent material 202a can be thicker along the edges to increase absorption in these regions to prevent leakage of fluid from the entire absorbent region 200. Other arrangements of layer thickness can be tailored to achieve specific absorption goals. Spaces between layers can be provided in the absorbent region 200, but more commonly the layers are closely aligned to each other. In an embodiment, the primary layer of absorbent material 202a and the secondary absorbent sheet 208 are compressed together to create a thinner cross section for the absorbent article 200.

[0060] As further shown in FIG. 2A, any specialized inner and outer layers may be added to the layered arrangement described above. For example, a top layer 212 of softer material may be included as a point of contact with the skin or other sensitive surface. This top layer 212 may include additives having advantageous properties, similar to those mentioned in connection with the top layer in FIG. 1: for example, additives that impart softness and excellent hand feel to the product, such as plasticizers (e.g., glycerin, PEG, Pluronic, etc.), or vitamins (e.g., Vitamin E) or drugs to treat diaper rash or other skin conditions, may be included in this inner layer. Desirably, the top layer 212 is permeable to the liquids 214 it encounters, so that the liquids 214 may be absorbed by the remainder of the absorbent region 200 without contacting the skin or other sensitive areas. Whether to add a specialized top layer 212 to the absorbent region and the properties of such specialized top layer 212 is a design decision based on the article of manufacture within which the absorbent region 200 is to be included. For example, personal care items such as diapers may be used with a specialized upper layer 212 that is in intimate contact with the subject's skin, as opposed to pads designed for minimal body contact applications, such as dog training pads, or pads where there is no or prolonged skin contact, such as disposable medical underpads.

[0061] A bottom layer 210 may be optionally applied to the absorbent region 200 as well. In embodiments, the bottom layer has barrier properties: for example, it may be water-resistant or waterproof and / or oil- and grease-resistant. Water, oil- and grease-resistant may be imparted by a number of techniques well known in the art, depending on the needs of the particular article of manufacture. For example, an outer waterproof layer for a personal care item may prevent any absorbed fluid from passing from the absorbent region 200 to the environment. Such a layer may also protect the absorbent region 200 from encountering fluids in the environment. Desirably, any special properties imparted to the outer layer 210 are produced using biopolymers, so that the entire article of manufacture is biodegradable.

[0062] FIG. 2B provides a top view of a primary layer of absorbent material 202b, which corresponds to a similar layer (202a) shown in cross-section in FIG. 2A. As shown in FIG. 2B, a plurality of apertures 204b are symmetrically arranged in an ordered geometric array, which generally corresponds to the ordered geometric array shown in FIG. 2A. However, it is understood that the apertures may be arranged in any ordered pattern, which may be to optimize the drainage and / or absorbency of the layer, or the apertures may be randomly arranged. Optional depressions or channels (not shown) may be formed on the surface in the absorbent material to direct fluid in the xy plane without the fluid penetrating the material in the z plane. A layer of absorbent material 202b that retains the arrangement of apertures may be formed by methods well known in the art. In an exemplary embodiment, such layers can be formed using the industrially standard reel-to-reel process, which is a well-established and economical manufacturing technique, especially when compared to air-laying. After formulation blending, the process can begin by pouring the entire formulation onto a moving silicone web (or other easy-to-release substrate, such as an olefin or Teflon belt). The liquid used to form the absorbent layer can be optionally squeezed through a narrow gap under a roller to define the final gel layer thickness. The continuous sheet then travels through a heating / drying tunnel or under a series of IR lamps. Many industrial drying options (e.g., microwave or vacuum-assisted evaporation) exist for this purpose. The dried sheet of absorbent material can be sandwiched between layers of paper, and the process can then be repeated the indicated number of times to produce a multi-layer stack. Those skilled in the art of reel-to-reel film manufacturing and multi-layer stacking can readily develop multiple mechanical alternatives or attachments to allow rapid, industrial-scale production of articles incorporating the inventive principles disclosed herein. Once a continuous stack roll is produced, it can be cut into portions that match the profile of the absorbent area for the article of manufacture, such as a diaper or personal care item or other absorbent article.The newly created edges of the layered stack resulting from cutting (e.g., by punching a hole with a sharp tool in one stroke) can optionally be pressed or otherwise bonded together to create a strong bond, resulting in a multi-layered stack core that behaves like a monolithic, integrated article.

[0063] In embodiments, as noted above, layers of absorbent material for use in forming absorbent regions for articles of manufacture can be patterned or pierced using conventional industrial techniques to create apertures, holes, channels, and the like to control fluid flow. For example, a layer of absorbent material can be prepared as a sheet that is partially or completely dried, and then the layer of absorbent material is pierced to create apertures, holes, or depressions in the surface. Alternatively, the absorbent material can be poured into a mold containing pore-forming elements and allowed to dry, such that when the material is removed from the mold, it contains impressions, channels, or holes that correspond to the pore-forming elements.

[0064] Various methods for forming apertures, holes or cavities in a sheet or layer of absorbent material are available besides perforation or molding. FIG. 2C shows a top view of a primary layer of absorbent material, which illustrates such an alternative embodiment, in which the apertures, holes or voids are formed by an overlay of overlapping strips, strands or blocks of absorbent material. As shown in FIG. 2C, the primary absorbent layer of the multi-layer structure of FIG. 2A can be formed with overlapping sections of absorbent material arranged in a preselected design, for example, a crisscross design. As shown in FIG. 2C, the bottom arrangement of vertical sections, strips or strands 220 of absorbent material can be covered by an overlay of horizontal sections, strips or strands 218 of absorbent material, or vice versa. Open areas 222 remain between the overlapping vertical and horizontal sections, strips or strands, which allows these gaps in the remodeled structure to act as holes extending into or through the layers. The primary absorbent layers shown in Figure 2C may be separated by one or more secondary absorbent sheets to form an organized multi-layer structure, such as that shown diagrammatically in Figure 2A. Although Figure 2C shows a geometrically ordered arrangement of overlapping vertical and horizontal sections, strips or strands, it is understood that any arrangement in which sections of absorbent material are overlaid on one another may result in apertures, holes, channels or other such gaps that allow fluid to pass through or be trapped in the layer. For example, elongated strands of absorbent material may be stacked on top of one another in an ordered or random manner, with apertures, holes or gaps thereby formed between the strands. In embodiments, the primary absorbent layer may be formed entirely from overlapping portions of absorbent material that create gaps between them that allow fluid to enter or pass through the layer, as shown in FIG. 2C, and in other embodiments, such layers may be formed that include regions or segments of overlapping portions of absorbent material that create gaps between them that allow fluid to enter or pass through the layer; such regions or segments may be embedded in other materials, which may be absorbent materials or may be carrier materials as previously described.

[0065] Specialized foaming techniques and foam products have been developed to form foam absorbent materials that can be used as layers to form the absorbent regions disclosed herein. Two exemplary foam morphologies have been identified that can be deployed to produce absorbent materials: (1) voids dispersed in a continuous gel layer that do not extend far enough to form in-plane or x / y connectivity, but are sufficient to create z-directional (i.e., thickness) penetration, thereby allowing the inflow fluid to spread into underlying layers, such as paper layers or other absorbent layers, as described in more detail below; and (2) co-continuous intertwining empty threads (e.g., elongated empty spaces) that are co-mixed with the biopolymer threads that make up the porous gel matrix, where both lateral and vertical spreading can occur rapidly within the gel layer. Control of the foam morphology can occur by varying the surfactant concentration in the formulation, adjusting the polymer concentration, and imposing a high degree of agitation, and then pouring the mixture onto a silicone substrate and drying to produce the final foamed (i.e., porous) sheet. The foamed material produced in either of the above configurations (1) or (2) has advantageous properties for use as an absorbent material. For example, when foaming occurs with dispersed voids (as described above in configuration (1)), the incoming liquid can wick down to the underlying paper layer and spread laterally quickly. This allows the layers of absorbent material above and below the paper layer to be efficiently exposed to the liquid, which can then be absorbed back by the previously unexposed areas of the gel layer.

[0066] In an embodiment, the formulation used to prepare the foam described above can include absorbent polymers, such as those described herein. For example, a mixture of hydroxyethyl cellulose (HEC) and hydroxypropyl methylcellulose (HPMC) can be used, and can be used in a ratio of 80:20, forming about 1.2% of the liquid formulation; the remainder of the liquid formulation is water, and plasticizers and surfactants added as described below. A plasticizer, such as glycerol, can be added to increase the flexibility of the final product, and can be added to the absorbent polymer solution, for example, at a plasticizer:absorbent polymer ratio of about 5:95. A glucoside surfactant can be added to the plasticizer-polymer solution, which facilitates the foaming process for the solution. Useful surfactants include hexyl glucoside and capryl glucoside, which can be added together or individually. One or more surfactants can be added at a surfactant:absorbent polymer ratio of about 1:1.5. Water is added to these components to form the total volume of the formulation. The mixture thus produced is stirred, thoroughly mixed, and then whipped or otherwise agitated to produce a foamed consistency for the formulation. The foamed formulation can then be spread to form a sheet, which can be dried in an oven to produce a final solid or semi-solid product, which can be used to prepare absorbent regions for articles of manufacture as described herein.

[0067] Additives for absorbable preparations Additives having advantageous properties may be included in the mixture of high viscosity hydrogel-forming polymer and plasticizer, and / or in the carrier layer, in the layered absorbent region, such as that described above with respect to FIG. 1, and in the layer of absorbent material itself, such as that described above with respect to FIG. 2. Desirably, compostable and biodegradable materials derived from renewable sources may be used as additives. A wide range of additives may be included, whether as particles, fluids or emulsions, including, but not limited to, activated carbon, activated carbon, zeolites, bicarbonate powders, solid desiccant powders, emulsified oils, and the like. Other desired additives may be envisioned by those skilled in the art.

[0068] More specifically, by way of example, materials such as activated charcoal, activated carbon or biochar (made from coconut shells or other natural materials) can be added as suspended particles into the hydrogel mixture to reduce odor and improve odor control, or the materials can be infused into one or more carrier layers, or both. Such materials are known to be porous and trap toxic chemicals and odors. In embodiments, odor-absorbing or odor-neutralizing chemicals (e.g., β-cyclodextrin, bicarbonate, pentane-1,5 diol, etc.), perfumes, fragrances and other odorant modifiers can be advantageously introduced into the hydrogel mixture or embedded in the carrier material, or both. Essential oils and other fragrances can be provided in encapsulated form (e.g., encapsulated in cyclodextrin) for inclusion in the absorbent material, carrier material, or both. The absorbent region containing the odor absorbing additive may be useful for personal care items such as diapers, incontinence pads and feminine hygiene products. In another embodiment, the absorbent region containing the odor absorbing additive may be useful for pet care products such as animal litter.

[0069] As another example, the additive can be a filler additive, such as fluff pulp, microfibrillated cellulose or nanofibrillated cellulose, which can reduce cost and / or contribute to a softer or more stable texture for the resulting absorbent material or carrier material or both. A softer, more conformable absorbent material can be used for bandages or personal care items, where shape and malleability can improve performance. For pet care products, softening additives can improve "paw feel", which is an important feature for products such as animal litter. As another example, bicarbonate or starch can be added to improve dimensional stability. As yet another example, additives that function as indicators can be used. Color-changing indicators can be used to indicate when the absorbent material or carrier material or both are saturated, for example, in diapers or for animal litter. Indicators can also be used for diagnostic purposes, where the indicator reveals the presence of a particular chemical in urine or a particular pH change in the absorbent material or carrier material or both. Such indicators may provide information about disease, disruptions in homeostasis, etc. for veterinary purposes (in animal litter) or for pediatric or geriatric patients using the absorbent article for personal care. Similarly, indicators in bandages comprising the absorbent materials disclosed herein may signal physiological changes when the absorbent material is exposed to bodily fluids.

[0070] Other additives with specialized properties can be included in the absorbent material or carrier material or both disclosed herein to produce a range of useful products through materials embedded in or attached to the matrix of the absorbent material or the matrix of the carrier material. For example, additives for personal care articles that are incorporated into the hydrogel itself or the carrier material can include plasticizers (e.g., glycerin, PEG, Pluronics, etc.) to impart softness and good hand feel to the product. As another example, skin rejuvenation ingredients (e.g., hyaluronic acid, aloe vera, alpha lipoic acid, and vitamins C and E) can be loaded into the hydrogel or embedded into the carrier material. Pharmaceuticals (e.g., hydrocortisone, antifungal agents) can be incorporated into the hydrogel or carrier material or both to create a vehicle for drug delivery, for example, to treat diaper rash or other skin conditions. In other embodiments, wound dressings may be prepared using the absorbent materials and combinations thereof disclosed herein, and additional agents may be included in the polymer layer or carrier material layer or both, such as preservatives, antimicrobial agents, blood clotting agents, etc. In embodiments, the hydrogel layer, either alone or in combination with a carrier layer, may be held proximate to or secured to the skin as a component of a bandage or dressing.

[0071] In embodiments, filler materials can be added to the hydrogel matrix to reduce material costs. For example, a polymer, such as low molecular weight dextrin, dextran or other low molecular weight carbohydrates, can be added to a mixture of high viscosity hydrogel-forming polymers and plasticizers, which additives can also expand as the hydrogel is formed. The expansion ability of the added filler can reduce the need for more expensive components in the absorbent matrix.

[0072] In embodiments, fillers and smaller oligomers can be used as fillers to reduce costs, but foaming can also be used to reduce costs and promote expansion. The formulations prepared as described above can be used, which include water-swellable polymers and plasticizers, but the mixture can be stirred and foam introduced into the viscous solution, thereby forming foam. In other embodiments, surfactants (e.g., non-ionic surfactants) can be used, instead of or in addition to vigorous stirring to allow for foam generation and subsequent foam formation. In embodiments, components known in the art to increase viscosity can be introduced into the mixture, as viscous solutions can promote foaming more easily. The addition of foam (foam) can increase the porosity of the hydrogel, thereby creating voids in which water can be absorbed and stored. This porosity within the hydrogel allows polymers with less inherent swelling to be used, but still promotes equivalent water entrapment. Other components of the formulations described above (e.g., crosslinkers) can be used in a similar manner to when the hydrogel is foamed.

[0073] The mixture of high viscosity hydrogel-forming polymers and plasticizers disclosed herein may be used as a coating on other particles or core materials to produce composite absorbent materials. The coating mixture may include additives, examples of which are described above. In certain embodiments, a porous core material is provided and may be partially or completely enveloped by the mixture. In other embodiments, the core material is substantially solid and non-porous and may be partially or completely enveloped by the mixture. Desirably, the core material may be selected from renewable materials. In embodiments, the core material imparts advantageous properties, such as stability, or improved odor uptake, to the coated composite structure. Useful core materials include, but are not limited to, natural materials, such as activated carbon, charcoal, biochar, walnut or other nut shells, sawdust, fluff pulp, corn bracts, psyllium husk, and the like. In embodiments, the core material is about 0.2 mm to about 5 mm in size, or about 0.2 to about 2 mm in size. In embodiments, the coating thickness is about 1 micron to about 100 microns thick and is applied either uniformly or non-uniformly on the surface of the core material. In embodiments, the coated particles can be produced by adding the core particles and a high viscosity hydrogel-forming mixture to a mixing tank and heating the resulting combination with a heating element or other similar equipment (oven, fluid bed dryer, etc.). During or after heating, the core particles are stirred or agitated in the mixture to separate them and allow for a uniform coating (not necessarily if a fluid bed dryer is used).

[0074] 5. Exemplary Articles of Manufacture a. Personal care items A variety of personal care articles can be formed using the intumescent materials and absorbent regions as disclosed herein, either separately or in combination with other non-intumescent materials in an arranged structure, such as the absorbent region described with respect to Figure 1. In embodiments, absorbent articles of manufacture, such as diapers, incontinence pads, feminine hygiene products, and the like, can be more economically formed, more conveniently and comfortably worn, and have performance characteristics, such as moisture wicking and retention of breathability, by incorporating absorbent regions, such as those described herein.

[0075] In embodiments, the use of expandable materials and absorbent regions formed from such expandable materials, all of which are disclosed herein, may improve the biodegradability or compostability of disposable personal care items, such as infant diapers or adult incontinence pads. By way of example, a conventional disposable diaper includes the following components: a topsheet or inner layer that contacts the infant's skin and forms the first point of contact for waste fluids; an absorbent core region that absorbs and retains waste fluids; and a waterproof backsheet or outer layer that provides a barrier that keeps fluids inside the diaper and provides leakage protection. The topsheet in a conventional disposable diaper is generally made of woven, non-woven, or porous formed-film polyethylene or polypropylene materials. The backsheet may be formed of the same material as the topsheet, but typically includes an inner film barrier that keeps fluids inside the diaper in addition to an outer surface that is soft to the touch. A SAP for fluid absorption is disposed in the absorbent core. The absorbent materials and absorbent regions formed therefrom, all of which are disclosed herein, when replacing conventional petroleum-derived SAP, are removed from the product, which impairs its biodegradability and compostability: thus making the product more sustainable, yet retaining the desired performance characteristics of the conventional version. Further improving sustainability, the petroleum-derived materials used in the topsheet and backsheet can be replaced with bio-based materials, which are themselves biodegradable and compostable, as described herein, aiming for a fully biodegradable and / or compostable disposable diaper. The absorbent regions disclosed herein can be incorporated into conventional diaper configurations, resulting in fully biodegradable and / or compostable articles of manufacture. Furthermore, the absorbent materials and absorbent regions formed therefrom, all of which are disclosed herein, can be incorporated into disposable structures, which can be used in other personal care products besides disposable baby diapers.

[0076] In an embodiment, an article of manufacture, such as a conventional diaper or personal care product configuration, can be modified to include a reusable outer covering and a disposable inner component including an absorbent region. In an embodiment, the configuration includes a reusable outer shell, such as a (semi-permanent) elastic mesh, and a (used-once) disposable integrated absorbent structure or absorbent region, which are formed from a bio-based absorbent material as disclosed herein. The elastic mesh is used to position the disposable absorbent inner structure proximal to an anatomically favorable region within the article of manufacture, which can wick and absorb bodily fluids away from their point of delivery. The anatomically favorable region is an area of ​​the article of manufacture that is expected to encounter bodily fluids to be absorbed, such as urine or feces for a personal care item, menstrual flow for a sanitary napkin, wound drainage for a medical or surgical dressing, etc. The removable and non-disposable absorbent inner structure allows for hygienic and efficient collection of bodily fluids, which can be easily disposed of during removal of the absorbent inner structure. When it is time to replace the core, the caregiver simply pulls open the shell to expose the core. Because the core is a thin profile paper-gel stack, the entire article can be rolled up and disposed of in a compost pile or trash bin. Optionally, the disposable absorbent inner structure can be secured to a reusable outer covering with a biodegradable adhesive, which can lightly secure the inner structure to the reusable outer structure.

[0077] In an embodiment, a disposable absorbent inner structure is formed to include at least the following layers: (a) a layer closest to the skin, i.e., a skin protective layer that wicks bodily fluids toward the inner absorbent core; (b) an absorbent region external to such layers, comprising absorbent material, which is disposed within a matrix formed of bio-based materials (wood pulp, fluff pulp, microfibrillated cellulose, etc.) as described herein, or disposed as a component within an organized multi-layer structure as described above; and (c) a hydrophobic layer external to such layers, such as a layer of hydrophobically treated paper, which retains moisture in the absorbent core region and prevents leakage. The absorbent structure includes (i) an inner skin protective layer, (ii) one or more absorbent layers including an absorbent material and an optional carrier material (absorbent core), and (iii) an outer hydrophobic layer, although the absorbent structure may be constructed as one single structure including layers of all three natures (such as those shown in FIG. 1) or as multiple layers, which provide therein the inner skin protective layer, the absorbent core, and the outer hydrophobic layer.

[0078] In an embodiment, the article comprising the reusable shell and absorbent core described herein can be formed with a very thin overall profile.The disposable absorbent inner structure consistent with the principles of the present invention can be formed so that when soiled, it can be changed / replaced without the need to change / replace the reusable mesh layer, which remains in place.Advantageously, the disposable core is thin and lightweight, making it convenient and comfortable to wear under clothing, for example, for adult incontinence pads.In addition, the small size and light weight of the product makes it suitable for business models, such as subscription-based home delivery, increasing convenient use.

[0079] The reusable outer covering can be made of materials such as stain-repellent cotton, mix-woven cotton with Lycra (stretchy cotton), polyester / cotton blends, athletic grade nylon, etc., which allow the covering to be washed and used for a long period of time. The outer mesh can be constructed to conform to the contours of the wearer's body and can be made of durable elastic materials (e.g., Lycra, spandex, silicone, etc.). This mesh architecture for the outer covering is highly breathable, since it is porous. In addition to the convenience of this approach, it can reduce skin contact time with waste products and reduce potential skin irritation issues such as diaper rash. In an embodiment, the fastener can be a metal clasp, which is durable, easy to use, and remodelable for repeated use. The design scheme can even be colorful and personal. The leg holes can have high-quality elastic bands to create a fit. To open the shell, one simply releases the metal clasp, opening the shell sufficiently to allow for collection of the used / soiled core, and a new core can be reapplied. Other modifications consistent with the purpose of the reusable outer covering and the commercial orientation of the product can be readily envisioned by those skilled in the art.

[0080] Advantageously, the absorbent core formed according to these systems and methods is made of naturally derived biodegradable materials, which can deliver exceptional performance.In an embodiment, the performance of absorbent core material is comparable to or better than most conventional disposable diapers, which are made of bulky, synthetic, non-degradable SAP (super absorbent polymer) beads and fluff pulp debonded by expensive hammer mill.In addition, while conventional disposable absorbent materials, such as those used in diapers and other personal care products, are typically manufactured by air-lamination, which is both capital and process intensive, the innovative core disclosed herein is manufactured using a well-established rapid continuous reel-to-reel process, significantly reducing the cost of goods.

[0081] The core-shell diaper configuration, made viable by the inventors' development of a proprietary biodegradable, highly absorbent, fast-wicking paper / gel multi-layer stack, has important ecological and sustainability implications. Not only is petroleum consumption (necessary to make synthetic SAP beads) substantially reduced or even eliminated, but the thin core is also fully compostable. Because the shell is reusable, this invention has the potential to save a significant amount (30% by some estimates) of future landfill volume, and it is believed that conventional disposable diapers can be substantially replaced by this novel technology.

[0082] Additional features can be introduced into the core-shell assembly. For example, the core can be "dammed" around the edges, for example by folding the edges (as mentioned in the previous section) before pressing to make the edges thicker and aid in waste containment. Multiple geometric and design features can be envisioned and incorporated to facilitate core-shell integration. All such improvements are intended to be within the spirit and scope of the present invention.

[0083] In embodiments, many design improvements and functional additives can be incorporated into and constructed from this basic invention. For example, functional additives, such as odor absorbents, can be incorporated into the gel layer or interspersed between layers. Or, for example, functional additives including natural ingredients, such as pulverized activated carbon (i.e., biochar made from pyrolysis of agricultural residues), β-cyclodextrin and chitosan biopolymers can be used. Similarly, functional additives, such as fragrances (e.g., citrus oil (d-limonene), lavender oil and several other essential oils for aromatherapy), can be included. In embodiments, functional additives, such as antibacterial and antifungal ingredients, can be optionally added to the gel. The top paper layer can include health and wellness sensors, such as pH, glucose dehydrogenase (diabetes detection), protein colorimetric assays (detection of early onset kidney failure), among many other urine-based laboratory test chemistries.

[0084] This approach to diaper and personal care product construction, using replaceable absorbent inserts similar to replaceable filters for coffee machines or vacuum cleaners, is already familiar to consumers and offers clear price and environmental benefits since only a small portion of the entire article requires disposal. By using biodegradable materials in the absorbent core instead of traditional synthetic SAP, the absorbent material is inherently less environmentally intolerable. By providing a smaller size absorbent core for disposal compared to traditional form factors for disposable diapers, the absorbent personal care product is suitable for small-scale composting instead of large-scale disposal facilities. Overall, this approach may enable an environmentally sustainable re-imagination of the entire disposable diaper industry.

[0085] b. Animal litter Materials for use in conventional animal litter (e.g. cat litter or "kitty litter") typically do not come from renewable resources. Clay materials predominate, particularly bentonite, such as sodium or calcium bentonite. Other clays added to animal litter mixtures are meerschaum, montmorillonite and kaolinite, depending on whether the formula is intended to clump when exposed to cat urine. Such materials are hydrated aluminum silicates, and trapped moisture creates a negative total ionic charge that attracts water and body fluids, resulting in fluid uptake and swelling of the material. In certain products, sodium silicate crystals are used in addition to or instead of clay. However, not all such materials are biodegradable or compostable. After use, animal litter materials are usually disposed of as municipal solid waste and have a millennium lifespan if committed to landfills.

[0086] The desired properties for animal litter include biodegradability, high rate of absorption and absorption volume capacity, adhesion, clumping ability, masking ammonia and other odors, density and texture acceptable to target animals, clumping strength, tendency to remain clumped, clumping weight and cost.By replacing conventional animal litter absorbents with the absorbent hydrogel material disclosed herein, biodegradable animal litter can be produced, which puts less strain on the environment.Biodegradable cat litter can be produced with the absorbent hydrogel material disclosed herein, which includes odor absorbing additives, in combination with other bio-based materials, which improve the texture, strength, dust protection, and / or cost of the final product.

[0087] c. Medical uses The absorbent materials disclosed herein can be adapted for multiple medical applications, such as wound treatment, blood clotting, treatment of skin conditions, surface application of medical or health treatments, and transdermal application of pharmaceutical treatments. These articles can be used as carriers for other active ingredients, such as pharmaceutical products, health agents, vitamins, nutrients, etc., to contact areas of the body that can benefit from exposure thereto. EXAMPLES

[0088] Working Example Materials and equipment used in Examples 1-5: ● Corning stirring plate ●BINDER forced convection oven ●Sigma Aldrich Chemicals ○Guar gum Pectin Dextrin Alginate Locust bean gum Glycerol Hydroxyethyl cellulose [HEC] Sodium chloride Calcium chloride Ammonium chloride Magnesium sulfate Sodium sulfate Sodium carboxymethylcellulose Other chemicals: ○Xanthan gum: Amazon ○Super absorbent beads: Amazon ○FILMKOTE 54: Ingredients ○ERYSIS GE-36: Huntsman Includes.

[0089] Example 1: One-dimensional biodegradable absorbent In this example, various natural polymers and compounds (listed in Table 2 below) were prepared in aqueous solutions at 5 wt.% concentration. Each solution was placed in multiple wells on a hemispherical silicone mold (1 cm diameter) and dried in a BINDER forced convection oven at 70°C. For the first set of tests, the resulting solid dry gels were tested for swelling ability by placing them in a small metal mesh cage, which was then submerged in a 0.104M simulated urine solution (prepared according to Table 1 below) at 25°C for 1 minute. The mesh cage was then removed from the urine solution, excess water was allowed to drip for 1 minute, and a paper towel was used to wipe off any remaining moisture around the cage, after which the weight of the swollen gel was measured. For the second set of tests, the experiment was reproduced under the same conditions (0.104M urine solution at 25°C), but the mesh cage containing the dry solid gel polymer / compound was submerged for 10 minutes to evaluate whether the natural polymer / compound continued to swell over time. The absorbent capacity for each sample was calculated according to EQ1 below and the resulting data are tabulated in Tables 2 and 3 for the 1 minute and 10 minute immersion experiments, respectively.

number

[0090] Example 2: Dual biodegradable absorbent Samples for this example were prepared by dissolving glycerol in DI water and then adding the natural polymer or compound listed in Table 4 at 2.5 wt.%. In each solution, glycerol was added at 10 wt.% of the natural polymer / compound weight. The drying protocol shown in Example 1 was followed for samples prepared from the polymers / compounds listed in Table 4, and the dried samples were tested using the 1 minute immersion protocol of Example 1, except the temperature of the simulated urine was 37° C. The results are summarized in Table 4 below. [Table 4]

[0091] Example 3: Ternary biodegradable absorbent In this example, a ternary system was prepared by dissolving glycerol in DI water and then adding a mixture of two natural polymers in the ratios shown in Table 5 for a combined concentration of 2.5 wt.%. Glycerol was added at 30 wt.% of the combined natural components. For example, a 300 g sample solution contained 290.25 g water, 2.25 g glycerol, 6.75 g HEC, and 0.75 g alginate.

[0092] The drying protocol set forth in Example 1 was followed for samples prepared from the polymer pairs listed in Table 5, and the dried samples were tested using the 1 minute immersion protocol of Example 1, except the temperature of the simulated urine was 37° C. The absorbent capacity for each pair of polymers is listed in Table 5 below. [Table 5]

[0093] Example 4: Natural absorbent polymers of various molecular weights Four different molecular weights of hydroxyethylcellulose (listed in Table 7) were prepared as 1 wt% aqueous solutions. Glycerol was also included in each solution at 10 wt% of the polymer mass. The samples were dried using the same procedure as in Example 1 and then tested in a 0.154M simulated urine aqueous solution as shown in Table 6. The drying protocol shown in Example 1 was followed for samples prepared from the four molecular weights of hydroxyethylcellulose listed in Table 7, and the dried samples were tested using the simulated urine of Table 6 using the 1 minute soaking protocol of Example 1, with a simulated urine temperature of 37°C. The calculated absorbent capacity for each sample is shown in Table 7. [Table 6] [Table 7]

[0094] Example 5: Covalently Crosslinked Natural Absorbable Polymers This example tests the ternary composition of hydroxyethyl cellulose, alginate and glycerol prepared as described in Example 3, both in uncrosslinked and crosslinked form. For the crosslinked form, a crosslinker (triglycidyl ether of propoxylated glycerin) and a catalyst (butyl triethyl ammonium chloride) were mixed into the hydroxyethyl cellulose / alginate / glycerol solution at 1 wt% of the combined weight of HEC and alginate. By way of example, a solution of hydroxyethyl cellulose, glycerol, alginate and crosslinker may contain the following components: 290.10 g DI water + 2.25 g glycerol + 6.75 g HEC + 0.75 g alginate + 0.075 g crosslinker + 0.075 g catalyst. The resulting mixtures (amalgam) were dried according to the drying protocol of Example 1, and each was tested using the 1 minute immersion protocol of Example 1, except that the temperature of the simulated urine was 37°C. The absorbent capacities of both the crosslinked and non-crosslinked samples are listed in Table 8 below. [Table 8]

[0095] Materials and equipment used in Examples 6-7: ● Corning stirring plate ●BINDER forced convection oven ●Mesh tea filter Syringe Syringe needle Beaker Deionized (DI) water ●Sigma Aldrich Chemicals Gelatin Sodium alginate (alginate salt) ○ Guar Dextrin Sodium chloride Calcium chloride Boric Acid Sodium tetraborate Glycerol Other chemicals: ○Xanthan gum (XG): Amazon ○Super absorbent beads: Amazon (ASIN B075DX8PZ2) ○Erisys GE-36 Includes.

[0096] Example 6: Expandable Beads This experiment was performed to generate hydrogel beads made from natural materials and to test the bead formation and measure the degree to which they swell when exposed to DI water.

[0097] Viscous solutions of hydrogel polymers (as specified in Table 9) were generated by weighing out specific ratios (all specified in Table 9) of polymer powders or single polymer powders (if non-mixtures were used), slowly adding the powders to DI water, and stirring the mixture on a stir plate for 15-20 minutes vigorously at first, then at a slower speed until all powders were dissolved and the solution was homogenous. Separately, 40 g of crosslinking solution was made by adding the crosslinker in powder form to DI water and mixing until all powders were dissolved (different for each test as specified in Table 1). The crosslinking solutions were gently stirred in a beaker on a stir plate, and about 3 ml of each viscous hydrogel solution (prepared as previously described) was dropped into the beaker. It was observed that the added hydrogel formed into beads almost immediately upon dropping into the CaCl2 crosslinking solution, whereas the other crosslinking solutions did not support bead formation in the same way. The hydrogel beads formed in the crosslinker solution were filtered on a mesh screen (if possible), washed thoroughly with DI water, and dried in a 60° C. oven overnight.

[0098] Hydrogel beads were formed using the procedure described above with various hydrogel components, hydrogel concentrations, hydrogel ratios and crosslinking techniques as shown in Table 9. These sample beads were then tested according to the following protocol:

[0099] Prior to testing, all samples were placed back in the oven at 60° C. for 15 minutes to ensure that no moisture was present on the beads. For each test, 30 g of test solution (either DI water or 0.9% NaCl solution at room temperature as specified in Table 2) was weighed into a beaker and approximately 0.2 g of beads from each test sample was weighed into a mesh tee filter. The mesh tee filter containing the beads was immersed in the beaker containing the test solution and gently swirled for 1 minute (XY direction only). After 1 minute, the mesh tee filter was removed and allowed to drain. The bottom of the filter was wiped with a paper towel and the beads were weighed again to determine liquid uptake and overall expansion. For the control, commercially available SAP beads were tested following the same protocol. The results for the control and sample tests, as well as observer comments, are shown as seen in Table 10. [Table 9] [Table 10-1] [Table 10-2]

[0100] Example 7: Extruded Chains A 10% mixture of hydroxyethyl cellulose and sodium alginate (80 / 20 ratio) can be made in a mixing tank by slowly adding the polymer powder to a 10% glycerol solution in DI water, stirring vigorously for 20 minutes, then stirring slowly until all the polymer is dissolved, producing a thick viscous solution. Erisys GE36 multifunctional epoxy crosslinker can then be added at 5% by weight of the total polymer addition. The hydrogel mixture with added crosslinker can be placed in an extruder with devolatilization capabilities and then extruded as chains of dehydrated cured polymer (with much of the water evaporated from the heating process in the extruder), where the chains are about 1 cm in diameter. The chains can be transferred to a conveyor oven where they can be heated at 60° C. for 2 hours. Upon removal from the oven, the chains can be cut into small cylindrical pellets (1 cm long) to form dry beads, or the chains can be cut into long chains about 3 inches long and about 1 cm in diameter. Other shapes and diameter to length ratios can be similarly prepared using similar techniques.

[0101] The pellets and strands can be tested in 0.9% NaCl solution at body temperature to test the swelling capacity. Possible swelling capacity results for beads about 1 cm in diameter can include about 1400-1600% weight gain. Possible swelling capacity for strands about 3 inches long can include about 1200-1400% weight gain.

[0102] Materials and equipment used in Examples 8, 9 and 10: Stirring plate ●VWR Forced Convection Oven ●OniLAB overhead stirrer ●Sigma Aldrich Chemicals Hydroxyethyl cellulose (HEC) ○(Hydroxypropyl)methylcellulose (HPMC), Mn~120,000 and Mn~10,000 Glycerol Capryl glucoside ThermoFischer extrusion machines (single or parallel screw) ●Slot die extrusion molding machine Doctor Blade ●Support Flat silicone sheet Flat carbon steel pan ○ Silicone mold with 200+ cavities Includes.

[0103] Example 8: Solution for Sheets In this example, a solution with absorbent properties was made and then spread into a sheet. The absorbent polymers (HEC and HPMC) were evaluated together at a concentration of 1.2% of the total solution (sum). The absorbent to glycerol ratio was equal to 95:5, the absorbent to surfactant (capryl glucoside) ratio was 1.5:1, and water made up the remaining volume of the solution. To prepare the solution, water was added to a beaker, then glycerol was added. The beaker was placed on a magnetic stir bar and stirred at medium shear for about 5 minutes. The surfactant was then added to the beaker, and the beaker was placed on an overhead stir bar at 150 rpm. The absorbent was then weighed and added to the beaker, and the rpm was increased to 300. The solution was mixed at 300 rpm for 5-10 minutes, then the mixing speed was returned to 150 rpm and allowed to stir overnight (about 12-24 hours). Once the solution was sufficiently homogenized, a doctor blade was used to spread the solution evenly onto either a carbon steel pan or a silicone mat as a support. The sheets were prepared to a thickness of 2 mm, but it is recognized that the thickness can be anywhere between about 0.5 mm and about 4 mm. The sheets were placed in a 70° C. oven to dry.

[0104] Once dry, the sheets were peeled off the support and cut into rectangular pieces for absorption testing. For this test, 0.9% NaCl was prepared in a water bath to mimic the composition of urine. A 425-micron sieve was added to the bath and the water reached approximately halfway up the top opening. Each sample of the sheet was weighed dry and then placed in a saline bath and allowed to sit for approximately 1 minute. The pieces were then removed from the water and weighed to determine the expansion of the samples. The expansion was determined by dividing the dry weight from the wet weight. The expansion data is listed in Table 11 below. [Table 11]

[0105] Example 9: Solutions and Carriers In this example, the solution was used to dispense onto a substrate. The polymer solution was made following the same protocol from Example 8. The polymer solution was added to an extruder / slot die and long strands of the solution were dispensed onto a paper towel, tissue paper or fluff pulp substrate. Most of the water evaporated during the extrusion heating process, leaving hardened polymer on the substrate. The samples were then placed in a 70°C oven and left to dry sufficiently. These samples were tested in a 0.9% NaCl solution bath for absorption as tested in Example 8 above.

[0106] Example 10: Polymer Networks The solution prepared according to Example 8 was used to generate a polymer network. After preparing the solution, the solution was dried on a silicone baking mold with many cavities, which allowed the solution to be embedded in the crevices and cavities in the x and y directions, resulting in a preselected network-like morphology. After drying, the mold was turned upside down and the dried material was released, preserving its morphological characteristics. The shaped material with its morphological characteristics was then placed in a 70°C oven and further dried. After sufficient drying, all shaped structures were placed in a 0.9% NaCl bath with a strainer / sieve underneath; the structures were left in the bath for 1 minute and then removed. The expansion was then recorded by dividing the wet weight by the dry weight. The shaped structures may be layered with paper towels, tissues, napkins or fluff pulp, and such shaped structures may have different shaped morphologies to provide different mechanical or absorbent properties to the specified layers and / or to facilitate the movement of fluids into or through the layers at different rates. The swelling data is listed in Table 3, and high MW HPMC polymers were used for these tests. [Table 12]

[0107] Example 11: Formulation for absorbent sheets In this example, HEC constituted 0.5-10% of the total solution, glycerol was added in a ratio of 95:5 HEC to glycerol, surfactant was added in a ratio of 1.5:1 HEC to capryl glucoside, and the remainder was water. First, glycerol was added to the water and placed on a magnetic stir bar for 5 minutes. Then, capryl glucoside was added to the glycerol water mixture and transferred to an overhead mixer. Finally, HEC was metered and slowly added to the mixture. The rpm of the overhead mixer was increased to 300 and held at this level for 5-20 minutes. The speed was then reduced to 150 rpm and the solution was stirred at this speed overnight to homogenize. The solution was then spread to a uniform thickness of 1.5 mm onto a silicone mat or carbon metal pan using a doctor blade and placed in an oven at 45° C. for 5 hours. When the sheet was removed from the oven, it was peeled off the substrate and cut into small rectangles for absorption testing. The test method described in Example 8 was carried out to measure how much the sheet expanded with water. The expansion data is listed in Table 13 below. [Table 13]

[0108] Example 12: Comparison of HEC:HPMC ratios Experiments were conducted to optimize the ratio of HEC to HPMC in the formulation. Solutions were prepared as in Example 8 with ratios of HEC:HPMC of 95:5, 90:10, 80:20, 70:30 and 60:40. These solutions were dried on silicone mats or carbon metal pans and tested for swelling using the same method as described in Example 8 above. The swelling data is listed in Table 14 below. [Table 14-1] [Table 14-2]

[0109] Example 13: Foam sheet In this example, a solution was prepared as described in Example 8. Once the solution was homogenous, it was poured into a small mixing bowl and beat with a whisk to generate foam. The solution, with the new foam, was then poured onto a silicone mat, allowed to dry, and tested for expansion as described in Example 8. The expansion data for the foamed sheet is listed in Table 15. [Table 15]

[0110] While the present invention has been particularly shown and described with respect to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and detail can be made therein without departing from the scope of the invention encompassed by the appended claims.

Claims

1. at least one hydrogel-forming swellable polymer, wherein said polymer is a cellulose ether; plasticizers; and surfactants An absorbent material comprising: The absorbent material is biodegradable.

2. The absorbent material described in claim 1, wherein the polyol is xylitol or glycerol.

3. The absorbent material of claim 1 further comprising a second plasticizer.

4. The absorbent material of claim 1 further comprising a cross-linking agent.

5. The absorbent material of claim 1, wherein the polymer is a mixture of cellulose ethers.

6. The absorbent material of claim 5, wherein the mixture of cellulose ethers is a mixture of hydroxyethyl cellulose (HEC) and hydroxypropyl methylcellulose (HPMC).

7. The plasticizer is glycerol or xylitol, 2. The absorbent material of claim 1, wherein the surfactant is selected from the group consisting of capryl glucoside and hexyl glucoside.

8. The plasticizer is glycerol or xylitol, 7. The absorbent material of claim 6, wherein the surfactant is selected from the group consisting of capryl glucoside and hexyl glucoside.

9. The absorbent material of claim 6, wherein the ratio of HEC to HPMC is from about 95:5 to about 60:

40.

10. The absorbent material of claim 9, wherein the ratio of HEC to HPMC is about 95:5 to 70:

30.

11. The absorbent material of claim 1, wherein the polymer is present in an amount of about 1% to 2% by weight.

12. The absorbent material of claim 6, wherein the polymer is present in an amount of about 1% to 2% by weight.

13. The absorbent material of claim 8, wherein the plasticizer is glycerol and the ratio of HEC to HPMC is from about 95:5 to about 60:

40.

14. The absorbent material of claim 13, wherein the plasticizer is glycerol and the ratio of HEC to HPMC is from 95:5 to 70:

30.

15. The absorbent material of claim 1, further comprising an additive, the additive being an odor-absorbing or odor-neutralizing chemical.

16. The absorbent material of claim 15, wherein the odor-absorbing or odor-neutralizing chemical is selected from the group consisting of activated carbon, activated carbon, biochar, beta-cyclodextrin, bicarbonate, and pentane-1,5 diol.

17. The absorbent material of claim 1, further comprising an additive, the additive being microfiberized cellulose or nanofiberized cellulose.

18. An article of manufacture comprising the absorbent material of any one of claims 1 to 17.

19. An article of manufacture dispensed onto a biodegradable carrier material.

20. The article of claim 18, wherein the biodegradable carrier material is derived from wood pulp.

21. The article of manufacture of claim 18, wherein the article is animal litter.

22. The article of manufacture of claim 21, wherein the absorbent material is formed as strands or fibers.

23. The article of manufacture of claim 21, wherein the article is cat litter.

24. The article of manufacture of claim 18, wherein the article is a pet training pad.

25. The article of manufacture of claim 18, wherein the absorbent material partially or completely encases the core material.

26. The article of manufacture of claim 25, wherein the core material is selected from the group consisting of activated carbon, charcoal, biochar, nut shells, sawdust, fluff pulp, corn bracts, and psyllium seed husks.

27. The article of manufacture of claim 18, wherein the absorbent material is formed as a sheet.

28. The article of manufacture of claim 18, wherein the absorbent material is formed as a fiber.

29. The article of manufacture of claim 18, wherein the absorbent material is foam.

30. The article of manufacture of claim 29, wherein the foamed absorbent material is expanded to form a sheet.

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