Nanoporous superabsorbent particles with low non-solvent levels

Abstract

Superabsorbent particles are provided that contain nanopores having a non-solvent of less than 1,000 ppm, a median size of about 50 to about 2,000 μm, and an average cross-sectional dimension of about 10 to about 500 nm. The superabsorbent particles exhibit a vortex time of about 80 seconds or less.

Description

Technology Field

[0001] The present invention relates to nanoporous superabsorbent particles having a low non-solvent level. Background Technology

[0002] Superabsorbent materials are used in a wide range of applications to aid in fluid absorption. These materials can generally absorb fluids (e.g., water, saline solution, etc.) in amounts several times their own weight. However, one problem associated with many conventional superabsorbent materials is that their absorption rate can be relatively slow when they first come into contact with a fluid.

[0003] As an effort to improve absorption rates, phase inversion of superabsorbent materials has been proposed. Phase inversion involves swelling of the superabsorbent material in a solvent, washing of the swollen superabsorbent material in a non-solvent, and removal of the non-solvent through drying. Although phase inversion produced superabsorbent materials with very rapid absorption rates, ( for example It has been found that large amounts of non-solvent (up to 13%) remain in superabsorbent materials, which can ultimately reduce the material's absorbency under load (AUL) and cause an unpleasant alcohol odor to be emitted from the material during use, and additionally, some jurisdictions have placed limits on the amount of non-solvent that may be present in certain types of products.

[0004] Therefore, it would be beneficial to provide a superabsorbent material with reduced non-solvent levels. In addition to improved absorption capacity under load, providing a superabsorbent material with reduced non-solvent levels would be another advantage.

[0005] According to one aspect of the present invention, superabsorbent particles are disclosed that contain a nonsolvent of less than about 1,000 ppm and have nanopores having a median size of about 50 to about 2,000 μm and an average cross-sectional dimension of about 10 to about 500 nm. The superabsorbent particles exhibit a vortex time of about 30 seconds or less.

[0006] Other features and aspects of the present invention will be described in more detail below. Brief explanation of the drawing

[0007] All possible disclosures of the present invention, including the best mode of the invention for a person skilled in the art, are described more specifically in the remainder of the specification where reference is made to the accompanying drawings. FIG. 1 illustrates an apparatus that can be used to measure the load absorption capacity ("AUL") of porous superabsorbent particles of the present invention; Figure 2 illustrates the AUL assembly of Figure 1. The repeated use of reference features in this specification and drawings is intended to indicate the same or similar features or elements of the invention. Specific details for implementing the invention

[0008] Now, one or more examples will be described below with reference to various embodiments of the present invention. Each example is provided for the purpose of illustrating the present invention, not to limit the invention. In practice, it will be obvious to those skilled in the art that various modifications and variations may be made to the present invention without departing from the spirit or scope of the invention. For example, features illustrated or described as part of one embodiment may be used in another embodiment to obtain another embodiment. Accordingly, the present invention is intended to include such variations and modifications within the scope of the appended claims and their equivalents.

[0009] Generally speaking, the present disclosure has discovered that by carefully controlling the formation of superabsorbent particles, substantially reduced levels of non-solvent can be retained in the superabsorbent particles after phase inversion treatment. In particular, as discussed in more detail below, the present disclosure has discovered that by initially drying the superabsorbent particles and then rehydrating them before re-drying or final drying, superabsorbent particles having very low levels of non-solvent are obtained while maintaining high porosity and rapid absorption characteristics. For example, in one aspect, the superabsorbent particles contain an amount of non-solvent of about 1000 ppm or less, e.g., about 900 ppm or less, e.g., about 800 ppm or less, e.g., about 700 ppm or less, e.g., about 600 ppm or less, e.g., about 500 ppm or less, e.g., about 400 ppm or less, e.g., about 300 ppm or less, e.g., about 200 ppm or less, e.g., about 100 ppm or less, e.g., about 50 ppm or less, e.g., about 30 ppm or less.

[0010] Additionally, in one aspect, the superabsorbent particles may have a median size (e.g., diameter) of about 50 to about 2,000 μm, in some embodiments about 100 to about 1,000 μm, and in some embodiments about 200 to about 700 μm. As used herein, the term "median" size refers to a "D50" size distribution of the particles, meaning that at least 50% of the particles have the indicated size. Likewise, the particles may have a D90 size distribution (at least 90% of the particles have the indicated size) within the ranges described above. The diameter of the particles may be determined using known techniques such as ultracentrifugation or laser diffraction. For example, the particle size distribution may be determined according to standard test methods such as ISO 13320:2009. The particles may also have any desired shape, such as flakes, nodules, spheres, tubes, etc. The size of the particles may be adjusted to optimize performance for specific applications. The specific surface area of ​​the particles can also be relatively large, for example, about 0.2 square meters / gram (m²). 2 / g) or more, in some embodiments about 0.6m 2 / g or more, about 1m in some embodiments 2 / g to about 5 m 2 / g, and is determined, for example, according to the BET test method described in ISO 9277:2010.

[0011] Regardless of the specific size or shape of the particles, superabsorbent particles are inherently porous and generally possess a porous network that may contain a combination of closed and open cell pores. The total porosity of the particles can be relatively high. For example, the particles are approximately 2 square meters / gram (m²). 2 / g) or more, in some embodiments about 5 to about 150m 2 / g, in some embodiments, about 15 to about 40 m 2The total pore area can be expressed in / g. The porosity percentage may also be about 5% or more, about 10% to about 60% in some embodiments, and about 15% to about 60% in some embodiments. Another parameter characteristic of porosity is bulk density. In this regard, the bulk density of the superabsorbent particles of the present invention is, for example, about 0.7 grams / cubic centimeter (g / cm²). 3 Less than ) about 0.1 to about 0.65 g / cm² in some embodiments 3 , in some embodiments, about 0.2 to about 0.6 g / cm³ 3 It can be determined at a pressure of 0.58 psi through the mercury intrusion method.

[0012] To achieve desired pore characteristics, the porous network contains a plurality of nanopores having average cross-sectional dimensions (e.g., width or diameter) of typically about 10 to about 500 nm, about 15 to about 450 nm in some embodiments, and about 20 to about 400 nm in some embodiments. The term “cross-sectional dimension” generally refers to a characteristic dimension (e.g., width or diameter) of a pore that is substantially orthogonal to the major axis (e.g., length) of the pore. It should be understood that a number of pore types may exist within the network. For example, micropores having average cross-sectional dimensions of about 0.5 to about 30 μm, about 1 to about 20 μm in some embodiments, and about 2 μm to about 15 μm in some embodiments may also be formed. Nevertheless, nanopores may be present in relatively high amounts in the network. For example, nanopores may constitute at least about 25 volume% of the total pore volume in the particles, at least about 40 volume% in some embodiments, and about 40 volume% to about 80 volume% in some embodiments. The average volume percentage occupied by nanopores within a given unit volume of the material is also cm³ of the particles. 3The ratio may be about 15% to about 80% per cubic centimeter, about 20% to about 70% in some embodiments, and about 30% to about 60% in some embodiments. A number of subtypes of nanopores may also be used. In certain embodiments, for example, a first nanopore may be formed having an average cross-sectional dimension of about 80 to about 500 nm, about 90 to about 450 nm in some embodiments, and about 100 to about 400 nm in some embodiments, while a second nanopore may be formed having an average cross-sectional dimension of about 1 to about 80 nm, about 5 to about 70 nm in some embodiments, and about 10 to about 60 nm in some embodiments. The nanopores may have any regular or irregular shape, such as spherical, elongated, etc. Nevertheless, the average diameter of the pores within the porous mesh will typically be about 1 to about 1,200 nm, about 10 nm to about 1,000 nm in some embodiments, about 50 to about 800 nm in some embodiments, and about 100 to about 600 nm in some embodiments.

[0013] Partially due to specific properties of the porous mesh and the method of forming superabsorbent particles, the inventors have discovered that the generated superabsorbent particles may exhibit an enhanced absorption rate during a specific period when they begin to come into contact with a fluid, e.g., water, an aqueous solution of salt (e.g., sodium chloride), or body fluid (e.g., urine, blood, etc.). This increased rate can be characterized in various ways. For example, the particles may exhibit a low vortex time, which is related to the amount of time in seconds required for the amount of superabsorbent particles to close the vortex generated by stirring a 0.9 wt% amount of sodium chloride solution according to the test described below. More specifically, the superabsorbent particles may exhibit a vortex time of about 80 seconds or less, about 60 seconds or less in some embodiments, about 40 seconds or less in some embodiments, about 35 seconds or less in some embodiments, about 30 seconds or less in some embodiments, about 20 seconds or less in some embodiments, and about 0.1 to about 15 seconds in some embodiments. Alternatively, after contact with an aqueous solution of sodium chloride (0.9 wt%) for 0.015 kiloseconds ("ks"), the absorption rate of the particles may be about 300 g / g / ks or more, about 400 g / g / ks or more in some embodiments, about 500 g / g / ks or more in some embodiments, and about 600 to about 1,500 g / g / ks in some embodiments. High absorption rates may even be maintained for a relatively long period. For example, after contact with an aqueous solution of sodium chloride (0.9 wt%) for 0.06 ks or even up to 0.12 ks, the absorption rate of the particles may still be about 160 g / g / ks or more, about 180 g / g / ks or more in some embodiments, about 200 g / g / ks or more in some embodiments, and about 250 to about 1,200 g / g / ks in some embodiments.

[0014] In particular, the increased absorption rate can be maintained without sacrificing the total absorption capacity of the particles. For example, after 3.6 ks, the total absorption capacity of the particles may be about 10 g / g or more, about 15 g / g or more in some embodiments, and about 20 to about 100 g / g in some embodiments. Likewise, the particles may exhibit a centrifuge retention capacity ("CRC") of about 20 g or more of liquid per gram of superabsorbent particle (g / g), about 25 g / g or more in some embodiments, and about 30 to about 60 g / g in some embodiments. Finally, the superabsorbent particles may also exhibit a free swell gel bed permeability ("GBP") of about 40 darcy or less, about 25 darcy or less in some embodiments, and about 0.1 to about 10 darcy in some embodiments.

[0015] Superabsorbent particles are generally formed of a three-dimensional cross-linked polymer network containing repeating units derived from one or more ethylenically (e.g., monoethylenically) unsaturated monomer compounds having at least one hydrophilic radical, e.g., carboxyl, carboxylic acid anhydride, carboxylic acid salt, sulfonic acid, sulfonic acid salt, hydroxyl, ether, amide, amino, or quaternary ammonium salt group. Specific examples of suitable ethylenically unsaturated monomer compounds for forming superabsorbent particles are, for example, carboxylic acids (e.g., (meth)acrylic acids (including acrylic acid and / or methacrylic acid), maleic acid, fumaric acid, crotonic acid, sorbic acid, itaconic acid, cinnamic acid, etc.); Salts of carboxylic acids (alkali metal salts, ammonium salts, amine salts, etc.) (e.g., sodium (meth)acrylate, trimethylamine (meth)acrylate, triethanolamine-(meth)acrylate, sodium maleate, methylamine maleate, etc.); vinyl sulfonic acids (e.g., vinylsulfonic acid, allyl sulfonic acid, vinyltoluene sulfonic acid, styrene sulfonic acid, etc.); (meth)acrylsulfonic acids (e.g., sulfopropyl (meth)acrylate, 2-hydroxy-3-(meth)acryloxypropyl sulfonic acid, etc.); salts of vinyl sulfonic acid or (meth)acrylsulfonic acid; alcohols (e.g., (meth)allyl alcohol); Ethers or esters of polyols (e.g., hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, poly(oxyethylene oxypropylene) glycol mono(meth)allyl ether (the hydroxyl group may be etherified or esterified), etc.); vinylformamide; (meth)acrylamide, N-alkyl (meth)acrylamide (e.g., N-methylacrylamide, N-hexylacrylamide, etc.), N,N-dialkyl (meth)acrylamide (e.g., N,N-dimethylacrylamide, N,N-di-n-propylacrylamide, etc.); N-hydroxyalkyl (meth)acrylamide (e.g., N-methylol(meth)acrylamide, N-hydroxyethyl-(meth)acrylamide, etc.);N,N-dihydroxyalkyl (meth)acrylamide (e.g., N,N-dihydroxyethyl (meth)acrylamide); vinyl lactam (e.g., N-vinylpyrrolidone); amino group-containing esters of carboxylic acids (e.g., dialkylaminoalkyl esters, dihydroxyalkylaminoalkyl esters, morpholinoalkyl esters, etc.) (e.g., dimenylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, morpholinoethyl (meth)acrylate, dimethylaminoethyl fumarate, etc.); heterocyclic vinyl compounds (e.g., 2-vinylpyridine, 4-vinylpyridine, N-vinylpyridine, N-vinylimidazole), etc.); Quaternary ammonium salt-containing monomers (e.g., N,N,N-trimethyl-N-(meth)acryloxyethylammonium chloride, N,N,N-triethyl-N-(meth)acryloyloxyethylammonium chloride, 2-hydroxy-3-(meth)acryloyloxypropyl trimethylammonium chloride, etc.); and others, as well as any combination of the foregoing. In most embodiments, (meth)acrylic acid monomer compounds as well as their salts are used to form superabsorbent particles.

[0016] The monomer compounds mentioned above are generally water-soluble. However, it should be understood that compounds capable of becoming water-soluble through hydrolysis may also be used. Suitable hydrolyzable monomers may include, for example, ethylenically unsaturated compounds having at least one hydrolyzable radical, such as esters, amides, and nitrile groups. Specific examples of such hydrolyzable monomers include methyl (meth)acrylate, ethyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, vinyl acetate, (meth)allyl acetate, (meth)acrylonitrile, etc. Additionally, it should be understood that additional monomers may be used so that the resulting particles are formed as copolymers, such as random, grafted, or block copolymers. If desired, the comonomer(s) may be selected from the group of monomers listed above. For example, the comonomer(s) may be (meth)acrylic acid, a salt of (meth)acrylic acid, maleic anhydride, etc. In one specific embodiment, for example, the copolymer may be formed from acrylic acid (or its salt) and maleic anhydride. In other embodiments, as described in more detail below, a comonomer containing a crosslinkable functional group such as an alkoxysilane may also be used. Regardless of the comonomer(s) used, the primary ethylenically unsaturated monomer(s) constitute at least about 50 mol% of the monomer used to form the polymer, about 55 mol% to about 99 mol% in some embodiments, and about 60 mol% to about 98 mol% in some embodiments, whereas the comonomer(s) generally prefer to constitute about 60 mol% or less of the monomer used to form the polymer, about 1 mol% to about 50 mol% in some embodiments, and about 2 mol% to about 40 mol% in some embodiments.

[0017] To form a network capable of absorbing water, it is generally desirable for the polymer to be crosslinked during and / or after polymerization. In one embodiment, for example, ethylenically unsaturated monomer compound(s) may be polymerized in the presence of a crosslinking agent to provide a crosslinked polymer. A suitable crosslinking agent typically has two or more groups that can react with the ethylenically unsaturated monomer compound and are at least partially water-soluble or water-dispersible, or at least partially soluble or dispersed in an aqueous monomer mixture. Examples of suitable crosslinking agents include, for example, tetraallyloxyethane, N,N'-methylene bisacrylamide, N,N'-methylene bismethacrylamide, trialylamine, trimethylolpropane triacrylate, glycerol propoxytriacrylate, divinylbenzene, N-methylol acrylamide, N-methylol methacrylamide, glycidyl methacrylate, polyethylene polyamine, ethyl diamine, ethyl glycol, glycerin, tetraallyloxyethane and pentaerythritol, trialyl ethers such as aluminates, silica, and alumosilicate, as well as combinations thereof. The amount of crosslinking agent may vary, but is typically present in an amount of about 0.005 to about 1.0 mol% based on the moles of the ethylenically unsaturated monomer compound(s).

[0018] In the embodiments described above, crosslinking generally occurs during polymerization. However, in other embodiments, the polymer may contain potential functional groups that can be crosslinked when desired. For example, the polymer may contain alkoxysilane functional groups that form silanol functional groups that condense to form a crosslinked polymer upon exposure to water. One specific example of such a functional group is a trialkoxysilane having the following general structure:

[0019]

[0020] Here, R1, R2 and R3 are independently alkyl groups having 1 to 6 carbon atoms.

[0021] To introduce such functional groups into a polymer structure, monomer compounds containing functional groups, such as ethylenically unsaturated monomers containing trialkoxysilane functional groups, may be used. Particularly suitable monomers are (meth)acrylic acid or its salts, such as methacryloxypropyl trimethoxysilane, methacryloxyethyl trimethoxysilane, methacryloxypropyl triethoxysilane, methacryloxypropyl tripropoxysilane, acryloxypropylmethyl dimethoxysilane, 3-acryloxypropyl trimethoxysilane, 3-methacryloxypropylmethyl diethoxysilane, 3-methacryloxypropylmethyl dimethoxysilane, 3-methacryloxypropyl tris(methoxyethoxy)silane, etc. In addition to a copolymerizable monomer containing a trialkoxysilane functional group, a copolymerizable monomer that can subsequently react with a compound containing a trialkoxysilane functional group, or a component that reacts with water to form a silanol group may also be used. These monomers may contain amines or alcohols, though not limited to these. The amine group incorporated into the copolymer may subsequently react with, for example, (3-chloropropyl)trimethoxysilane, though not limited to this. The alcohol group incorporated into the copolymer may subsequently react with, for example, tetramethoxysilane, though not limited to this.

[0022] The superabsorbent polymer particles of the present invention may be produced by any known polymerization method. For example, the particles may be produced by any suitable bulk polymerization technique, such as solution polymerization, reverse suspension polymerization, or emulsion polymerization, as described, for example, in U.S. Patents No. 4,076,663, 4,286,082, 4,340,706, 4,497,930, 4,507,438, 4,654,039, 4,666,975, 4,683,274, or 5,145,906. In solution polymerization, for example, monomer(s) are polymerized in an aqueous solution. In reverse suspension polymerization, monomer(s) are dispersed in an alicyclic or aliphatic hydrocarbon suspension medium in the presence of a dispersant, such as a surfactant or a protective colloid. If desired, the polymerization reaction may be carried out in the presence of a free radical initiator, a redox initiator (reducing and oxidizing agent), a thermal initiator, a photoinitiator, etc. Examples of suitable reducing agents may include, for example, ascorbic acid, alkali metal sulfites, alkali metal bisulfites, ammonium sulfites, ammonium bisulfites, alkali metal hydrogen sulfites, ammonium hydrogen sulfites, iron metal salts, for example, ferrous sulfate, sugars, aldehydes, primary and secondary alcohols, etc. Examples of suitable oxidizing agents may include, for example, hydrogen peroxide, caprylyl peroxide, benzoyl peroxide, cumene peroxide, tertiary butyl diperphthalate, tertiary butyl perbenzoate, sodium percarbonate, sodium peracetate, alkali metal persulfate, ammonium persulfate, alkyl hydroperoxide, perester, diacryl peroxide, silver salt, etc.

[0023] If desired, the generated particles can also be downsized to achieve the aforementioned desired size. For example, particles can be formed using impact downsizing, which typically utilizes a grinder equipped with rotary grinding elements. Repeated impact and / or shear stresses can be generated between the rotary grinding elements and the stationary or counter-rotating grinding elements. Additionally, impact downsizing may use an airflow to transport the material to and impact the grinding disc (or other shear element). One particularly suitable impact downsizing device is marketed by Pallmann Industries (Clifton, New Jersey) under the designation Turbofiner®, Type PLM. In this equipment, a highly active air vortex is generated within a cylindrical grinding chamber between the stationary grinding elements and the rotary grinding elements of the impact grinding mill. Due to the high volume of air, the particles are impacted and downsized to the desired particle size. Other suitable impact downsizing processes are all Pallmann This may be described in U.S. Patents No. 6,431,477 and No. 7,510,133. Another suitable microparticle forming process is cold extrusion miniaturization, which generally uses shear and compressive forces to form particles of a desired size. For example, the material may be forced through a die at a temperature below the melting point of the matrix polymer. Solid-state shear grinding is another suitable process that can be used. This method involves the continuous extrusion of the material, generally under high shear and compressive conditions, while the extruder barrel and screw are cooled to prevent the polymer from melting. Examples of such solid-state grinding techniques are, for example, U.S. Patent Khait No. 5,814,673 of; Furgiuele et al. No. 6,479,003 of; Khait et al. No. 6,494,390 of; Khait No. 6,818,173 of; and Torkelson et al.It is described in U.S. Publication No. 2006 / 0178465. Another suitable fine particle formation technique is known as cryogenic disc milling. Cryogenic disc milling generally uses a liquid (e.g., liquid nitrogen) to cool or freeze the material before and / or during milling. In one embodiment, a single sliding disc milling apparatus having a stationary disc and a rotating disc may be used. The material enters between the discs through a channel near the center of the disc and is formed into particles through the frictional force generated between the discs. One suitable cryogenic disc milling apparatus is commercially available by ICO Polymers (Allentown, Pennsylvania) under the name Wedco® Cryogenic Milling System.

[0024] Although not strictly necessary, additional components may also be combined with the superabsorbent polymer before, during, or after polymerization. In one embodiment, for example, high aspect ratio inclusions (e.g., fibers, tubes, sheets, wires, etc.) may be used to help create an internal interlocking reinforcing framework that stabilizes the swollen superabsorbent polymer and improves its elasticity. The aspect ratio (average length divided by the median width) may be in the range of, for example, about 1 to about 50, about 2 to about 20 in some embodiments, and about 4 to about 15 in some embodiments. These inclusions may have a central width (e.g., diameter) of about 1 to about 35 μm, in some embodiments about 2 to about 20 μm, in some embodiments about 3 to about 15 μm, and in some embodiments about 7 to about 12 μm, as well as a volume average length of about 1 to about 200 μm, in some embodiments about 2 to about 150 μm, and in some embodiments about 5 to about 100 μm, and in some embodiments about 10 to about 50 μm. Examples of such high aspect ratio inclusions may include high aspect ratio fibers (also known as "whiskers") derived from carbides (e.g., silicon carbide), silicates (e.g., wollastonite), etc.

[0025] If desired, the hydrophobic material may also be combined with superabsorbent polymers, such as materials containing hydrocarbon groups, materials containing hydrocarbon groups having fluorine atoms, or materials having a polysiloxane structure. Examples of such materials and superabsorbent particles formed therefrom are, for example, Fujimura, etc.As described in U.S. Patent No. 8,742,023, which is incorporated herein by reference in its entirety. For example, suitable hydrophobic materials may include polyolefin resins, polystyrene resins, waxes, long-chain fatty acid esters, long-chain fatty acids and their salts, long-chain aliphatic alcohols, long-chain aliphatic amides, as well as mixtures thereof. In a specific embodiment, long-chain fatty acid esters may be used, such as esters of fatty acids having 8 to 30 carbon atoms and alcohols having 1 to 12 carbon atoms, for example, methyl laurate, ethyl laurate, methyl stearate, ethyl stearate, methyl oleate, ethyl oleate, glycerol monolaurate, glycerol monostearate, glycerol monooleate, pentaerythritol monolaurate, pentaerythritol monostearate, pentaerythritol monooleate, sorbitol monolaurate, sorbitol monostearate, sorbitol monooleate, sucrose monopalmitate, sucrose dipalmitate, sucrose tripalmitate, sucrose monostearate, sucrose distearate, sucrose tristearate, talo, etc. In other embodiments, long-chain fatty acids containing 8 to 30 carbon atoms or their salts, such as lauric acid, palmitic acid, stearic acid, oleic acid, dimer acid, behenic acid, etc., as well as their zinc, calcium, magnesium, and / or aluminum salts, such as calcium palmitate, aluminum palmitate, calcium stearate, magnesium stearate, aluminum stearate, etc., may be used.

[0026] Regardless of the specific method by which the particles are formed, various different techniques may also be used to form a porous network within the pre-formed particles. In a specific embodiment, for example, a technique known as "phase inversion" may be used, in which a polymer dissolved or swollen in a continuous-phase solvent system is inverted into a continuous-phase solid macromolecular network formed by the polymer. This inversion may be induced by various methods, such as solvent removal via a drying process (e.g., evaporation or sublimation), the addition of a non-solvent, or the addition of a non-solvent via a wet process. In the drying process, for example, the temperature (or pressure) of the particles may be altered so that the solvent system (e.g., water) can be converted to another state of matter that can be removed without excessive shrinkage by exhausting or purging the solvent system with gas. For example, freeze-drying involves cooling the solvent system below its freezing point and then sublimating it under reduced pressure to form pores. Meanwhile, supercritical drying involves heating the solvent system under pressure above the supercritical point to form pores.

[0027] However, the wet process is particularly suitable in that it does not rely on a significant amount of energy to achieve the desired inversion. In the wet process, the superabsorbent polymer and solvent system may be provided in the form of a single-phase homogeneous composition. The concentration of the polymer is typically in the range of about 0.1 to about 20 wt% / volume of the composition, and in some embodiments, about 0.5 to about 10 wt% / volume. The composition is then brought into contact with a non-solvent system using any known technique, such as immersion in a water bath, backwashing, spray washing, belt spraying, and filtering. The difference in chemical potential between the solvent and non-solvent systems causes molecules of the solvent to diffuse from the superabsorbent polymer, and molecules of the non-solvent to diffuse into the polymer. Ultimately, this causes the polymer composition to undergo a transition from a single-phase homogeneous composition to an unstable two-phase mixture containing polymer-rich and polymer-deficient fractions. In the polymer-rich phase, droplets of colloidal particles from the non-solvent system also serve as nucleation sites, are coated with polymer, and precipitate at specific points to form a continuous polymer network. The solvent composition within the polymer matrix also self-decomposes to form cavities. Subsequently, the matrix is ​​dried to remove the solvent and non-solvent systems, forming stable porous particles.

[0028] The exact solvent and non-solvent systems used to achieve phase inversion are not particularly important as long as they are selected together based on their miscibility. More specifically, the solvent and non-solvent systems may be selected to have a specific difference in Hildebrand solubility parameters (δ), which are predictive indicators of the miscibility of two liquids, generally having a higher value indicating a more hydrophilic liquid and a lower value indicating a more hydrophobic liquid. In general, the difference in Hildebrand solubility parameters between the solvent system and the non-solvent system (e.g., δ 용매 - δ비용매 ) is about 1 to about 15 calories 1 / 2 / cm 3 / 2 , in some embodiments, about 4 to about 12 calories 1 / 2 / cm 3 / 2 , in some embodiments, about 6 to about 10 calories 1 / 2 / cm 3 / 2 It is desirable that the solvent / non-solvent have sufficient miscibility for solvent extraction to occur, but will not be so miscible that phase inversion cannot be achieved. Solvents suitable for use in the solvent system may include, for example, water, aqueous alcohols, saline solution, glycerol, etc., as well as combinations thereof. Similarly, non-solvents suitable for use in the non-solvent system may include acetone, n-propyl alcohol, ethyl alcohol, methanol, n-butyl alcohol, propylene glycol, ethylene glycol, etc., as well as combinations thereof. In one aspect, the non-solvent includes methanol, ethanol, isopropyl alcohol, or a combination thereof.

[0029] Typically, the volume ratio of the solvent system to the non-solvent system is in the range of about 50:1 to about 1:200 (volume per volume), in some embodiments about 10:1 to about 1:180 (volume per volume), in some embodiments about 1:1 to about 1:160 (volume per volume), in some embodiments about 1:60 to about 1:150 (volume per volume), in some embodiments about 1:1 to about 1:60 (volume per volume), and in some embodiments about 1:1 to about 1:2 (volume per volume).

[0030] After contact with the non-solvent and phase inversion are completed, the liquid phase may be dried and / or removed by any suitable techniques, such as increased temperature, time, vacuum, and / or flow control using any suitable equipment (e.g., forced air oven and vacuum oven). In one embodiment, for example, the superabsorbent particles were high-temperature dried for a time sufficient to evaporate all of the sample except for about 30 wt.% or less ethanol, for example, about 25 wt.% or less ethanol, for example, about 20 wt.% or less ethanol, for example, about 16 wt.% ethanol, at a temperature of about 80°C or higher, e.g., about 90°C or higher, e.g., about 100°C or higher, e.g., about 110°C or higher, e.g., about 120°C or higher, e.g., about 130°C or higher, e.g., about 140°C or higher, e.g., about 150 wt.% or less ethanol, for example, about 175°C or any range or value between these, at a temperature of about 80°C or higher, e.g., about 90°C or higher, e.g., about 100°C or higher, e.g., about 110°C or higher, e.g., about 120°C or higher, e.g., about 130°C or higher, e.g., about 140°C or higher, e.g., about 150 wt.% or less ethanol, e.g., about 16 wt.% ethanol. However, in one aspect, the superabsorbent particles can instead be dried until the superabsorbent particles have a temperature of at least about 75% of the drying temperature, for example, at least about 80%, for example, at least about 85%, for example, at least about 90%, for example, at least about 95%, for example, at least about 99% of the drying temperature.

[0031] Nevertheless, as described above, after the superabsorbent particles are initially dried, the superabsorbent particles are rehydrated to a moisture level of about 10% to about 40% by weight, e.g., about 15% to about 35% by weight, e.g., about 20% to about 30% by weight, or any range or value between these, e.g., a water moisture level. In particular, the present disclosure has discovered that rehydrating the superabsorbent particles to a specific moisture level allows a non-solvent to pass through the superabsorbent particles without sacrificing the porous structure or rapid absorption characteristics.

[0032] However, in one aspect, the present disclosure further discovered that the desired moisture level may be based on the molecular weight of the non-solvent. For example, non-solvents with higher molecular weights may escape most efficiently toward the upper end of the cited range, whereas non-solvents with lower molecular weights may escape at lower moisture levels.

[0033] Regardless of the selected rehydration ratio, rehydration can be performed by spraying, immersion, or exposure to a humid environment, etc. A humid environment may be provided by any known method known in the art having the ability to control a humid environment at ambient or elevated temperatures. For example, a humidity chamber, a fluidized bed, or a tray dryer. Additionally, in one aspect, one or more methods may be selected. For example, superabsorbent particles may first be sprayed with water and then placed in a humid environment until a desired moisture level is reached.

[0034] In one aspect, when a humid environment is used, a humidified environment having a relative humidity of about 40% or more, e.g., about 50% or more, e.g., about 60% or more, e.g., about 70% or more, up to about 90%, or any range or value between these may be used. Humidification may be performed at room temperature or may be subjected to heat in addition to relative humidity of about 40°C to about 100°C, e.g., about 50°C to about 90°C, e.g., about 60°C to about 80°C, or any range or value between these.

[0035] Regardless of the moisture level and method used, after rehydration, the superabsorbent particles can be dried again to a target moisture level of about 1% to about 12.5% ​​by weight, e.g., about 1.5% to about 11% by weight, e.g., about 2% to about 10% by weight, or any range or value between these.

[0036] In addition, in one aspect, superabsorbent particles can be subjected to surface crosslinking treatment with a surface crosslinking agent. Surface crosslinking treatment can increase the gel strength of superabsorbent particles and improve the balance of CRC and GBP.

[0037] As a surface crosslinking agent, any conventional surface crosslinking agent (polyglycidyl, polyhydric alcohol, polyhydric amine, polyhydric aziridine, polyhydric isocyanate, silane coupling agent, alkylene carbonate, polyhydric metal, etc.) may be used. Among these surface crosslinking agents, considering economic efficiency and absorption characteristics, the surface crosslinking agent is preferably polyglycidyl, polyhydric alcohol, or polyhydric amine. The surface crosslinking agent may be used alone or as a mixture of two or more of these.

[0038] When surface crosslinking treatment is performed, the amount (weight%) of the surface crosslinking agent used is not particularly limited, as the amount may vary depending on the type of surface crosslinking agent, crosslinking conditions, target performance, etc. When considering absorption characteristics, the amount is preferably 0.001 to 3 weight%, more preferably 0.005 to 2 weight%, and particularly preferably 0.01 to 1 weight% based on the weight of the superabsorbent particles.

[0039] Surface crosslinking treatment is performed by mixing superabsorbent particles with surface crosslinking agent(s) and then heating. Suitable processes are described in more detail in Japanese Patent No. 3648553, JP-A-2003-165883, JP-A-2005-75982, and JP-A-2005-95759, each of which is incorporated herein by reference to the extent that it does not conflict with the present specification. Mixing the superabsorbent polymer with the surface crosslinking agent may be performed using any suitable equipment including any conventional equipment (cylinder-type mixer, screw-type mixer, screw-type extruder, turbulator, Nauta mixer, kneader mixer, flow-type mixer, V-type mixer, grinder, ribbon mixer, air-flow-type mixer, disc-type mixer, conical blender, rolling mixer). The surface crosslinking agent may be diluted with water and / or a solvent.

[0040] The temperature at which the superabsorbent particles and the surface crosslinking agent are mixed is not particularly limited. The temperature for mixing the superabsorbent particles with the surface crosslinking agent is preferably 10 to 150°C, more preferably 20 to 100°C, and most preferably 25 to 80°C.

[0041] Surface crosslinking of superabsorbent particles can be performed under heat after mixing with a surface crosslinking agent. The temperature for surface crosslinking is preferably 100 to 180°C, more preferably 110 to 175°C, and most preferably 120 to 170°C. The heating time for surface crosslinking can be appropriately controlled based on the temperature. In terms of absorption performance, the surface crosslinking time is preferably 5 to 60 minutes, and more preferably 10 to 40 minutes.

[0042] Surface crosslinking of superabsorbent particles can be performed before and / or after the phase inversion process, as well as before or after the rehydration process. However, in one aspect, surface crosslinking can be performed before the phase inversion process to avoid aggregation of superabsorbent particles during the phase inversion process. However, to further improve the balance between CRC and GBP, surface crosslinking can be performed after the phase inversion process. Thus, in one aspect, surface crosslinking can be performed before and after the phase inversion process and / or, depending on the focus of the crosslinking, before or after rehydration.

[0043] The present invention can be better understood by referring to the following examples.

[0044] Test method

[0045] Qi Gong characteristics

[0046] The pore characteristics of superabsorbent particles (e.g., average pore diameter, total pore area, bulk density, pore size distribution, and porosity) may be determined using mercury porosiometers (also known as mercury intrusion), as is well known in the industry. For example, commercially available porosiometers, such as Micrometrics’ AutoPore IV 9500, may be used. These devices typically characterize porosity by applying varying levels of pressure to a sample impregnated with mercury. The pressure required to inject mercury into the pores of the sample is inversely proportional to the pore size. Measurements can be performed at an initial pressure of 0.58 psi and a final pressure of approximately 60,000 psi. The average pore diameter, total pore area, and bulk density can be measured directly during the mercury intrusion test. The overall pore size distribution can be derived from a graph of differential intrusion versus pore diameter (μm). Similarly, porosity can be calculated based on the reduction in bulk density (assuming constant particle size, packing, and shape), taking into account that approximately 50% of the volume is occupied by empty space due to particle packing. More specifically, porosity can be determined according to the following equation:

[0047] 100 x 0.5 x [(Bulk density of control sample - Bulk density of test sample) / Bulk density of control sample]

[0048] Here, bulk density (g / cm³) 3 ) is determined by mercury intrusion at a pressure of 0.58 psi.

[0049] absorption capacity

[0050] The absorption capacity of superabsorbent particles can be measured using the AUL (Absorbency Under Load) test, which is a well-known test for measuring the ability of superabsorbent particles to absorb a 0.9 wt% sodium chloride solution (test solution) in distilled water at room temperature while the material is under load. For example, 0.16 g of superabsorbent particles [show] a load absorption capacity (AUL) of 5.07 cm under nominal pressures of 0.01 psi, 0.3 psi, or 0.9 psi. 2 It may be confined within an area. The sample is allowed to absorb the test solution from a dish containing an excess amount of fluid. At predetermined time intervals, the vacuum device removes any excess void fluid from the cylinder and then weighs the sample. Then, using this weight-to-time data, the absorption rate is determined at various time intervals.

[0051] Referring to FIG. 1, an embodiment of a device (910) that can be used, for example, to determine an absorption capacity is illustrated. The device (910) comprises an AUL assembly (925) having a cylinder (920), a piston (930), and a weight (990). The weight (990) may have a weight of 100 grams. A side arm flask (960) may be used in which a rubber stopper (945) and a tube (955) are fitted to the top of the flask to help capture any fluid removed from the sample before the sample enters a vacuum system. A rubber or plastic tube (970) may be used in the side arm flask (960) and the AUL chamber (940). An additional tube (970) may also be used to connect the side arm (980) of the flask (960) to a vacuum source (not shown). Referring to FIG. 2, the cylinder (920) can be used to accommodate superabsorbent particles (950) and may be manufactured from an acrylic tube with an inner diameter of 1 inch (2.54 cm) that is slightly machined to ensure concentricity. After machining, a mesh cloth (414) (e.g., 400 mesh) may be attached to the bottom of the cylinder (920) using a suitable solvent to ensure the screen adheres securely to the cylinder. The piston (930) may be a 4.4 g piston made of a solid material (e.g., acrylic) with a diameter of 1 inch (2.5 cm) and may be machined to fit snugly into the cylinder (920) without being constrained. As previously described, the device (910) also includes an AUL chamber (940) for removing interstitial liquid absorbed during the swelling of the superabsorbent particles (950). This test apparatus is similar to the GATS (Gravity Absorption Test System) available from M / K Systems and the system described by Lichstein on pages 129–142 of the INDA Technological Symposium Proceedings of March 1974. Also, 2.A potted disc (935) having a port confined within a 5 cm diameter area is used.

[0052] To perform the test, you can follow these steps:

[0053] (1) Wiping the inside of the AUL cylinder (920) with an antistatic cloth and weighing the cylinder (920), weight (990) and piston (930);

[0054] (2) A step of recording the weight as the weight of the container in grams, in milligrams;

[0055] (3) A step of slowly pouring a sample of 0.16 ± 0.005 grams of superabsorbent particles (950) into a cylinder (920) so that the particles do not come into contact with the sides of the cylinder or adhere to the walls of the AUL cylinder;

[0056] (4) weighing the cylinder (920), weight (990), piston (930), and superabsorbent particle (950), and recording the value on the scale in grams as the dry weight, in milligrams;

[0057] (5) A step of gently tapping the AUL cylinder (920) until the super-absorbent particles (950) are evenly distributed on the bottom of the cylinder;

[0058] (6) Step of slowly placing the piston (930) and weight (990) into the cylinder (920);

[0059] (7) A step of placing a test fluid (a 0.9 wt% sodium chloride aqueous solution) in a fluid tank having a large mesh screen on the bottom;

[0060] (8) A step of simultaneously starting a timer and placing the superabsorbent particles (950) and the cylinder assembly (925) on a screen in a fluid tank. The level in the tank should be made of a height to provide at least 1 cm of head above the base of the cylinder;

[0061] (9) A step of gently swirling the sample to release any trapped air and ensuring that the superabsorbent particles come into contact with the fluid.

[0062] (10) removing the cylinder (920) from the fluid tank at specified time intervals and immediately placing the cylinder in the vacuum device (potted disk (935) on the upper part of the AUL chamber (940)) and removing excess gap fluid for 10 seconds;

[0063] (11) Step of wiping the outside of the cylinder with a paper towel or tissue;

[0064] (12) immediately weighing the AUL assembly (i.e., cylinder (920), piston (930) and weight (990)) with superabsorbent particles and any absorbed test fluid, and recording the weight as wet weight in grams at the most recent milligram and time intervals; and

[0065] (13) A step that is repeated for the required time interval.

[0066] At least two samples are typically tested at respective predetermined time intervals. The time intervals are typically 15, 30, 60, 120, 300, 600, 1800, and 3600 seconds (or 0.015, 0.030, 0.060, 0.120, 0.300, 0.600, 1.8, or 3.6 kiloseconds). At a specified time interval, the "absorption capacity" of the superabsorbent particles is calculated in grams of liquid relative to grams of superabsorbent using the following formula:

[0067] (Wet weight - Dry weight) / (Dry weight - Container weight)

[0068] absorption rate

[0069] The "absorption rate" of superabsorbent particles can be determined by dividing the aforementioned absorption capacity by a specific time interval (kilsecond, ks), such as 0.015, 0.030, 0.060, 0.120, 0.300, 0.600, 1.8, or 3.6 kiloseconds (g / g).

[0070] Centrifuge Retention Capacity (CRC)

[0071] The Centrifugal Retention Capacity (CRC) test measures the ability of superabsorbent particles to retain liquid after saturation and centrifugation under controlled conditions. The resulting retention capacity is expressed as grams of liquid retained per gram of sample weight (g / g). Samples to be tested are prepared as particles that are pre-screened through a U.S. Standard 30-mesh screen and retained on a U.S. Standard 50-mesh screen. Particles can be pre-screened manually or automatically and stored in a sealed, airtight container until testing. Retention capacity is measured by placing a pre-screened sample of 0.2 ± 0.005 g into a permeable bag containing the sample, allowing the test solution (0.9 wt% sodium chloride in distilled water) to be freely absorbed by the sample. Heat-sealed tea bag materials, such as heat-sealed filter paper of model designation 1234T, may be suitable. This bag is formed by folding a 5-inch x 3-inch sample of the bag material in half and heat-sealing two of the open edges to form a 2.5-inch x 3-inch rectangular pouch. The heat-sealed sections may be located approximately 0.25 inches inside the edges of the material. After placing the sample inside the pouch, the remaining open edges of the pouch may also be heat-sealed. Empty bags may be made to serve as controls. Prepare three samples (e.g., filled and sealed bags) for testing. Test the filled bag within 3 minutes of preparation unless it is placed immediately in a sealed container; in this case, the filled bag must be tested within 30 minutes of preparation.

[0072] Place the bags between two TEFLON® coated fiberglass screens with a 3-inch opening (Taconic Plastics, Inc., Petersburg, NY) and immerse them in a pan of test solution at 23°C, ensuring the screens are kept down until the bags are completely wetted. After wetting, leave the samples in the solution for approximately 30 ± 1 minute, at which point remove the samples from the solution and place them temporarily on a non-absorbent flat surface. For multiple tests, the pan must be emptied and refilled with fresh test solution after 24 bags have been saturated in the pan.

[0073] Then, the wet bags were placed in the basket of a suitable centrifuge capable of applying a g-force of approximately 350 to the samples. One suitable centrifuge is the Heraeus LaboFuge 400, which features a water collection basket, a digital rpm gauge, and a mechanical drain basket suitable for holding and draining the bag samples. When centrifuging multiple samples, the samples must be positioned facing each other inside the centrifuge to balance the baskets during rotation. The bags (including the wet empty bags) are centrifuged at approximately 1,600 rpm (e.g., to achieve a target g-force of approximately 350) for 3 minutes. The bags are removed and weighed, first weighing the empty bags (controls) and then weighing the bags containing the samples. Considering the solution held by the bag itself, the amount of solution held by the sample is the sample's centrifugal holding capacity (CRC), expressed as grams of fluid per gram of sample. More specifically, the centrifugal holding capacity is determined as follows:

[0074] Weight of sample bag after centrifugation - Weight of empty bag after centrifugation - Weight of dry sample

[0075] Dry sample weight

[0076] Three samples are tested, and the results are averaged to determine the retention capacity (CRC) of the superabsorbent material. The samples are tested at 23°C and 50% relative humidity.

[0077] vortex time

[0078] Vortex time is the time (in seconds) required for a predetermined mass of superabsorbent particles to close a vortex generated by stirring 50 ml of a 0.9 wt% sodium chloride solution at 600 rpm on a magnetic stirring plate. The time required for the vortex to close is an indication of the particles' free swelling absorption rate. The vortex time test can be performed at a temperature of 23°C and a relative humidity of 50% according to the following procedure:

[0079] (1) 50 ml (± 0.01 ml) of 0.9 wt% sodium chloride solution is measured in a 100 ml beaker.

[0080] (2) Place a ringless 7.9 mm x 32 mm TEFLON® covered magnetic stirring rod (e.g., commercially available as single-pack round stirring rods of the brand S / P® with a removable pivot ring) in a beaker.

[0081] (3) Program a magnetic stirring plate (e.g., commercially available as DATAPLATE® Model #721) to 600 rpm.

[0082] (4) Place the beaker in the center of the magnetic stirring plate so that the magnetic stirring rod is activated. The bottom of the vortex should be near the top of the stirring rod. Superabsorbent particles are pre-screened through a US standard #30 mesh screen (0.595 mm opening) and retained on a US standard #50 mesh screen (0.297 mm opening).

[0083] (5) Weigh the required mass of the superabsorbent particles to be tested on a weighing paper.

[0084] (6) While the sodium chloride solution is being stirred, quickly pour the absorbent polymer to be tested into the saline solution and start the stopwatch. The superabsorbent particles to be tested must be added to the saline solution between the center of the vortex and the side of the beaker.

[0085] (7) Stop the stopwatch and record the time when the surface of the saline solution becomes flat. The time recorded in seconds is recorded as the vortex time.

[0086] Free Swelling Gel Layer Permeability (GBP) Test

[0087] As used herein, the Free Swelling Gel Layer Permeability (GBP) test determines the permeability of the swollen layer of a superabsorbent material under conditions generally referred to as "free swell." The term "free swell" means that the superabsorbent material becomes capable of swelling without a swelling inhibition load upon absorption of the test solution, as described below. This test QinAs described in U.S. Patent Publication No. 2010 / 0261812, which is incorporated herein by reference. For example, a test apparatus comprising a sample container and a piston may be used, which may include a cylindrical LEXAN shaft having a concentric cylindrical hole drilled along the longitudinal axis of the shaft. Both ends of the shaft may be machined to provide an upper and a lower end. A weight may be placed on one end having a cylindrical hole passing through at least a portion of the center. A circular piston head may be located at the other end and may have a concentric inner ring of seven holes, each having a diameter of about 0.95 cm, and a concentric outer ring of fourteen holes, each having a diameter of about 0.95 cm. The holes are drilled from the top to the bottom of the piston head. The bottom of the piston head may also be covered with a biaxially extendable mesh stainless steel screen. The sample container may include a cylinder and a 100 mesh stainless steel cloth screen that is tightly biaxially stretched and attached to the bottom of the cylinder. Superabsorbent particles may be supported on the screen inside the cylinder during testing.

[0088] The cylinder may be drilled from a transparent Lexan rod or equivalent material, or cut from a Lexan tube or equivalent material, with an inner diameter of approximately 6 cm (e.g., approximately 28.27 cm). 2The cross-sectional area is, the wall thickness is about 0.5 cm, and the height is about 5 cm. A drain hole is formed in the side wall of the cylinder at a height of about 4.0 cm above the screen to allow liquid to be discharged from the cylinder, thereby maintaining the fluid level in the sample container at about 4.0 cm above the screen. The piston head can be machined from a Lexan rod or equivalent material and has a diameter sized to fit inside a cylinder with a height of about 16 mm and a minimum wall gap, while still allowing it to slide freely. The shaft can be machined from a Lexan rod or equivalent material and has an outer diameter of about 2.22 cm and an inner diameter of about 0.64 cm. The top end of the shaft is about 2.54 cm long and has a diameter of about 1.58 cm, forming an annular shoulder to support an annular weight. The annular weight, in turn, has an inner diameter of about 1.59 cm, slides over the top end of the shaft, and rests on the annular shoulder formed thereon. The annular weight can be manufactured of stainless steel or other suitable corrosion-resistant material in the presence of a test solution which is a 0.9 wt% sodium chloride solution in distilled water. The combined weight of the piston and the annular weight is approximately 596 g, which is about 28.27 cm. 2 Approximately 0.3 psi, or approximately 20.7 dynes / cm² across the sample area 2 It corresponds to the pressure applied to the sample. As described below, when the test solution flows through the test apparatus during the test, the sample container is typically placed on a 16-mesh rigid stainless steel support screen. Alternatively, the sample container may be placed on a support ring substantially the same diameter as the cylinder so that the support ring does not restrict flow from the bottom of the container.

[0089] To perform the Gel Bed Permeability Test under "free swell" conditions, a piston placed on top is positioned within an empty sample container, and the height from the bottom of the weight to the top of the cylinder is measured to the nearest 0.01 mm using an accurate caliper or a suitable gauge. The height of each sample container can be measured in an empty state, and the piston and weight used when multiple test devices are utilized can be tracked. If the sample swells later after saturation, the same piston and weight may be used for measurement. The sample to be tested is prepared with superabsorbent particles that are pre-screened through a US Standard 30-mesh screen and retained on a US Standard 50-mesh screen. The particles can be pre-screened manually or automatically. Approximately 0.9 g of the sample is placed in the sample container, and then the container without the piston and weight is immersed in the test solution for a period of about 60 minutes to saturate the sample and swell it without any restraining load. At the end of this period, the piston and weight assembly is placed on the saturated sample within the sample container, and then the sample container, piston, weight, and sample are removed from the solution. The thickness of the saturated sample is determined by re-measuring the height from the bottom of the weight to the top of the cylinder using the same caliper or gauge previously used, provided that the zero point does not change from the initial height measurement. The height measurement obtained by measuring the empty sample container, piston, and weight is subtracted from the height measurement obtained after saturating the sample. The resulting value is the thickness of the swollen sample, or height "H".

[0090] Permeability measurement is initiated by passing a flow of the test solution into a sample container containing a saturated sample, a piston, and a weight. The flow rate of the test solution into the container is regulated to maintain a fluid height of approximately 4.0 cm above the bottom of the sample container. The amount of solution passing through the sample versus time is measured by gravimetric measurement. Once the fluid level stabilizes and the height is maintained at approximately 4.0 cm, data points are collected every second for at least 20 seconds. The flow rate (Q) through the swollen sample is determined in units of grams per second (g / s) by the linear least squares method of fluid (grams) passing through the sample versus time (second). Permeability is obtained by the following equation:

[0091] K = (1.01325 x 10 8 ) * [Q*H*Mu] / [A*Rho*P]

[0092] Here

[0093] K = Permeability (again),

[0094] Q = flow rate (g / sec),

[0095] H = Sample height (cm),

[0096] Mu = liquid viscosity (poise) (approximately 1 centipoise for the test solution used in this test),

[0097] A = Cross-sectional area for liquid flow (cm²) 2 ),

[0098] Rho = liquid density (g / cm³) 3 ) (For the test solution used in conjunction with this test, approximately 1 g / cm³ 3 ), and

[0099] P = Hydrostatic pressure (dynes / cm²) 2 ) (Usually approximately 3,923 dynes / cm 2 ), this Rho*g*h It can be calculated as, where Rho = liquid density (g / cm³) 3 ), g = acceleration due to gravity, nominal 981 cm / s 2, and h = fluid height, e.g. 4.0 cm.

[0100] At least three samples are tested, and the results are averaged to determine the permeability of the free-swelling gel layer of the samples. The samples are tested at 23°C and 50% relative humidity.

[0101] moisture percentage

[0102] To measure the moisture percentage in superabsorbent particles, a moisture analyzer of the A & D Model MX50 was used. The moisture percentage was determined using a heating temperature of 140°C.

[0103] Quantification of non-essential agents in SAM

[0104] 0.03 g of SAM was placed in a 40 mL vial, followed by the addition of 17 g of water. The vial was then capped and placed in a wrist-operated shaker for 30 minutes. The vial was then removed from the shaker and homogenized for 1 minute. 3 mL of the homogenized mixture was transferred to a syringe and filtered through a glass fiber / 0.45 μm nylon membrane into a 2 mL GC autosampler vial to capture 0.5 to 1 mL of filtrate. The filtrate was analyzed for non-solvent content using the FC-FID methodology.

[0105] Analytical method conditions for non-solvent quantification

[0106] Equipment: Agilent 6890 GC

[0107] Column: DB-ALC1, 30 m x 0.53 mm x 3.0 μm film

[0108] Carrier gas: Nitrogen

[0109] Injector: 0.5 μL @ 5:1 split, temperature 250°C

[0110] Detector: FID @ 300C

[0111] Temperature Program: 40C for 3 minutes, maintain for 5 minutes up to 200C at 25C / minute

[0112] Runtime: 14.4 minutes

[0113] Retention time: Methanol - 1.8 min, Ethanol - 2.4 min, IPA - 2.9 min

[0114] Correction for quantification

[0115] Prepared standards containing methanol, ethanol, and isopropyl alcohol: 7 standards, 1-200 ppm, R2≥0.99.

[0116] Example 1A

[0117] 5 kg of commercially available cross-linked polyacrylate superabsorbent particles were initially provided. The particles Fujimura, etc. It was formed in the manner described in U.S. Patent No. 8,742,023 and had an initial vortex time of 35 seconds and a CRC of approximately 27.5 g / g. The particles were swollen with 50 kg of 20 wt% ethanol in water (the ethanol used was denatured to isopropyl alcohol). The swollen SAM particles were washed with 25 kg of ethanol denatured to isopropyl alcohol using a vacuum filtration system to remove excess liquid. This was repeated four more times. Initial drying of the sample occurred at a temperature of 170°C for 6 hours.

[0118] After initial drying, the superabsorbent particles were placed in a humid environment with a relative humidity of 60% and a temperature of 69°C for 4 hours. After rehydration, the superabsorbent particles had a moisture percentage of 29%. Then, the superabsorbent particles (SAM) were dried again at 65°C for 30 minutes.

[0119] Example 1B

[0120] Particles were formed as described in Example 1A, except that the particles were placed in a humid environment for 12 hours. After rehydration, the superabsorbent particles had a moisture percentage of 28%.

[0121] Example 1C

[0122] Particles were formed as described in Example 1A, except that the particles were placed in a humid environment for 48 hours. After rehydration, the superabsorbent particles had a moisture percentage of 27%.

[0123] Example 1 - Comparative Example

[0124] Particles were formed as described in Example 1A, except that the particles were not placed in a humid environment or dried again. The results of Example 1 are shown in Table 1.

[0125] yes Vortex [300-600 μm] (sec) Ethanol (ppm) in SAM Isopropanol (ppm) in SAM 1A 20 <28 <28 1B 19 <28 <28 1C 22 <28 <28 1-Control group 16 71299 3383

[0126] Example 2A - Comparative Example

[0127] 10 kg of commercially available cross-linked polyacrylate superabsorbent particles were initially provided. The particles Fujimura, etc. It was formed in the manner described in U.S. Patent No. 8,742,023 and had an initial vortex time of 35 seconds and a CRC of approximately 27.5 g / g. The particles were swollen with 90 kg of deionized water. The swollen SAM particles were washed with 100 kg of methanol using a vacuum filtration system to remove excess liquid. This was repeated two more times. Another 13.6 kg of methanol used to wash the particles was vacuum filtered to remove excess liquid. Initial drying of the samples was performed under vacuum at 80°C for 1 hour and at 140°C for 4 hours. Then, the particles were rehydrated for 2.4 hours in a humid atmosphere with a relative humidity of 20% and a temperature of 69°C. After rehydration, the particles had a moisture percentage of 6%. However, the particles were not dried again.

[0128] Example 2B - Comparative Example

[0129] Particles were formed as described in Example 2A, except that 40% relative humidity was used. After rehydration, the particles had a moisture percentage of 12%.

[0130] Example 2C - Comparative Example

[0131] Except for the particles being maintained in a humid atmosphere for 64 hours, particles were formed as described in Example 2B. After rehydration, the particles had a moisture percentage of 11%.

[0132] Yes 2D

[0133] Particles were formed as described in Example 2A, except that the humid air had a relative humidity of 60%. After rehydration, the particles had a moisture percentage of 27%.

[0134] Yes 2E

[0135] Except for drying the particles again on a hot plate at 140℃, particles were formed as described in Example 2D.

[0136] Example 2 - Comparative Example

[0137] Particles were formed as described in Example 2A, except that the particles were not placed in a humid environment or dried again. The results of Example 2 are shown in Table 2.

[0138] yes Vortex [300-600 μm] (sec) Methanol (ppm) in SAM 2A 18 63951 2B 17 13466 2C 17 997 2D 15 Not detected 2E 26 224 2-control group 16 66259

[0139] Example 3A - Comparative Example

[0140] 40 kg of commercially available cross-linked polyacrylate superabsorbent particles were initially provided. The particles Fujimura etc.It was formed in the manner described in U.S. Patent No. 8,742,023 and had an initial vortex time of 35 seconds and a CRC of approximately 27.5 g / g. The particles were swollen with 400 kg of 20 wt% ethanol in water. The swollen SAM particles were washed with 200 kg of ethanol using a vacuum filtration system to remove excess liquid. Another 100 kg of ethanol was used with the vacuum filtration system to remove excess liquid. The 100 kg ethanol wash was repeated five more times. Initial drying of the sample occurred at 120°C for 1 hour, followed by drying at 150°C for 1 hour, then drying at 170°C for 1 hour, and additionally, the particles were rehydrated at 80°C for 2 hours at approximately 50% relative humidity. After rehydration, the particles had a moisture percentage of 7%. The particles were not dried again.

[0141] Example 3B - Comparative Example

[0142] Particles were formed as described in Example 3A, except that the particles were rehydrated for 4 hours. After rehydration, the particles had a moisture percentage of 10%.

[0143] Example 3C - Comparative Example

[0144] Particles were formed as described in Example 3A, except that the particles were rehydrated for 6 hours. After rehydration, the particles had a moisture percentage of 11%.

[0145] Example 3D - Comparative Example

[0146] Particles were formed as described in Example 3A, except that the particles were rehydrated for 6 hours. Then, the particles were dried again at 80°C for 1 hour. After re-drying, the particles had a moisture percentage of 6%.

[0147] Yes 3E

[0148] 5 kg of commercially available cross-linked polyacrylate superabsorbent particles were initially provided. The particles Fujimura etc. It was formed in the manner described in U.S. Patent No. 8,742,023, had a particle size distribution of 90 to 300 μm, and underwent surface cross-linking during the formation process. The particles were mixed with 10 kg of denatured ethanol. Then, 10 kg of water was added and mixed for 5 minutes. An additional 30 kg of water was added to further swell the particles. The swollen SAM particles were washed several times with denatured ethanol using a vacuum filtration system to remove the access liquid. The particles were washed with ethanol until approximately 1 wt% water was measured in the collected access liquid. Initial drying of the samples occurred at 120°C for 1 hour and at 170°C for 2.5 hours. The particles were rehydrated at 70–75°C for 6 hours at approximately 50–62% relative humidity. After rehydration, the particles had a moisture percentage of 17%. Then, the particles were dried again at 70°C for 1 hour.

[0149] Yes 3F

[0150] Particles were formed as described in Example 3E, except that the particles were initially dried at 170°C for 3.5 hours. Then, the particles were rehydrated at 70°C for 6 hours at approximately 76% relative humidity. After rehydration, the particles had a moisture percentage of 30%. Then, the particles were dried again at 70°C for 1 hour.

[0151] Example 3 - Comparative Example

[0152] Particles were formed as described in Example 3A, except that the particles were not placed in a humid environment or dried again. The results of Example 3 are shown in Table 3.

[0153] yes Vortex [current particle size] (seconds) Ethanol (ppm) in SAM 3A 22 73562 3B 18 65578 3C 17 67154 3D 16 63034 3E 7 117215 3F 9 Not detected 3-Control group 17 112837

[0154] Example 4A

[0155] 50 kg of commercially available cross-linked polyacrylate superabsorbent particles were initially provided. The particles Fujimura etc. It was formed in the manner described in U.S. Patent No. 8,742,023, had a particle size distribution of 90 to 300 μm, and underwent surface crosslinking during the formation process. The particles were mixed with 100 kg of denatured ethanol. Then, 100 kg of water was added and mixed for 5 minutes. An additional 300 kg of water was added to further swell the particles. The swollen SAM particles were washed several times with denatured ethanol using a vacuum filtration system to remove the access liquid. The particles were washed with ethanol until approximately 1 wt% of water was measured in the collected access liquid.

[0156] The particles were initially dried in a fluidized bed at 160°C and maintained until the particle temperature reached 130°C. The particles were discarded from the fluidized bed. The particles were reintroduced into the fluidized bed for 3.5 hours using a humidifying gas to fluidize the particles until a moisture percentage of 19% was reached at a particle temperature of 76°C. The particles were not dried again.

[0157] Example 4B

[0158] The particles were placed in a fluidized bed using a humidifying gas for 4.5 hours and formed as described in Example 4A, except that the particles reached 23% moisture % at a particle temperature of 77°C. The particles were not dried again.

[0159] Yes 4C

[0160] The particles were placed in a fluidized bed using a humidifying gas for 5.5 hours and formed as described in Example 4A, except that the particles reached 28% moisture at a particle temperature of 77°C. Then, the particles were dried again at 70-90°C for 7.5 hours, and the final moisture percentage was 5%.

[0161] yes Vortex [current particle size] (seconds) Ethanol (ppm) in SAM 4A 6 22265 4B 8 855 4C 8 Not detected

[0162] Although the present invention has been described in detail with respect to specific embodiments of the invention, a person skilled in the art will understand that, by understanding the foregoing, alternatives, modifications, and equivalents to these embodiments can be easily conceived. Accordingly, the scope of the present invention should be evaluated as the claims and their equivalents.

Claims

Claim 1 A superabsorbent particle containing nanopores having a median size of 50 to 2,000 μm and an average cross-sectional dimension of 10 to 500 nm, wherein the superabsorbent particle contains less than 1,000 ppm of non-solvent; and wherein the superabsorbent particle exhibits a vortex time of 80 seconds or less, wherein the median size refers to the D50 size distribution of the particle, meaning that at least 50% of the particle has the indicated size, and wherein the superabsorbent particle has a moisture level of 1% to 12.5% ​​by weight. Claim 2 In claim 1, the particles are superabsorbent particles containing less than 500 ppm of non-solvent. Claim 3 Superabsorbent particles according to claim 1 or 2, wherein the particles exhibit an absorption rate of 300 g / g / ks or more after being placed in contact with a 0.9 wt% aqueous sodium chloride solution for 0.015 kiloseconds. Claim 4 The superabsorbent particles according to claim 1 or 2, wherein the superabsorbent particles exhibit an absorption rate of 500 g / g / ks or more after being placed in contact with a 0.9 wt% aqueous sodium chloride solution for 0.015 kiloseconds. Claim 5 The superabsorbent particles according to claim 1 or 2, wherein the superabsorbent particles exhibit an absorption rate of 160 g / g / ks or more after being placed in contact with a 0.9 wt% aqueous sodium chloride solution for 0.120 kiloseconds. Claim 6 The superabsorbent particles according to claim 1 or 2, wherein the superabsorbent particles exhibit a total absorption capacity of 10 g / g or more after being placed in contact with a 0.9 wt% aqueous sodium chloride solution for 3.6 kiloseconds. Claim 7 In claim 1 or 2, the particles are superabsorbent particles having a centrifugal retention capacity of 20 g / g or more. Claim 8 The superabsorbent particle according to claim 1 or 2, wherein the particle further contains micropores, said micropores having an average cross-sectional dimension of 0.5 to 30 μm. Claim 9 The superabsorbent particle according to claim 1 or 2, wherein the nanopores constitute at least 25 volume% of the pores within the particle. Claim 10 In claim 1 or 2, the particle is 2m 2 Superabsorbent particles exhibiting a total pore area of ​​1 / g or more. Claim 11 In claim 1 or 2, the particles are superabsorbent particles exhibiting a porosity of 5% or more. Claim 12 In claim 1 or 2, the particle is 0.7 g / cm³ determined at a pressure of 0.58 psi by the mercury intrusion method. 3 Superabsorbent particles exhibiting a bulk density of less than [amount]. Claim 13 In claim 1 or 2, the particles are superabsorbent particles having an average pore diameter of 1 to 1,200 nm. Claim 14 In claim 1 or 2, the particle is 0.2 m, determined according to ISO 9277:2010. 2 Superabsorbent particles having a specific surface area of ​​1 / g or more. Claim 15 A method for forming superabsorbent particles of claim 1 or 2, the method comprising: forming a composition containing a superabsorbent polymer and a solvent system; contacting the composition with a non-solvent system to initiate the formation of pores through phase inversion; drying the superabsorbent particles; and rehydrating the particles to a moisture level of 10% to 40% by weight based on the weight of the superabsorbent particles. Claim 16 In claim 15, the method wherein the superabsorbent particles are rehydrated to a moisture level of 15% to 35% by weight. Claim 17 In paragraph 15, the method wherein the superabsorbent particles are rehydrated by spraying, immersion, placement in a humid atmosphere, or a combination thereof. Claim 18 A method that further includes a reconstruction step in Clause 15. Claim 19 In claim 15, the method wherein the non-solvent comprises acetone, n-propyl alcohol, ethanol, methanol, n-butyl alcohol, propylene glycol, ethylene glycol, or a combination thereof. Claim 20 Superabsorbent particles formed according to the method of paragraph 15.

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