Superabsorbent polymers and methods for their preparation

Abstract

Provided are superabsorbent polymers and methods of making the same, and more particularly, provided are superabsorbent polymers capable of exhibiting improved bacterial growth inhibition characteristics without degrading the water retention capacity of the superabsorbent polymers and methods of making the same.

Description

Technical Field

[0001] Cross-reference to related applications

[0002] This application is based on and claims priority to Korean Patent Application Nos. 10-2021-0120837 and 10-2022-0103399, filed on September 10, 2021 and August 18, 2022, respectively, the disclosure of which is incorporated herein by reference in its entirety.

[0003] This invention relates to superabsorbent polymers and their preparation methods, wherein the superabsorbent polymers exhibit improved bacterial growth inhibition properties without degrading their absorption performance. Background Technology

[0004] Superabsorbent polymers (SAPs) are synthetic polymer materials capable of absorbing 500 to 1000 times their own weight in water. Different manufacturers use various names for them, such as SAM (SuperAbsorbency Material) and AGM (Absorbent Gel Material). Since their initial application in hygiene products, SAPs are now widely used not only in hygiene products such as baby diapers, but also in water-retaining soil products for horticulture, waterproofing materials for civil engineering and construction, seedling sheets, preservatives in food processing, and materials for mud dressings.

[0005] In particular, superabsorbent polymers have been widely used in hygiene products such as baby diapers, adult diapers, and disposable absorbent products. Therefore, when bacteria grow in these hygiene products and disposable absorbent products, there are problems with secondary odors and various diseases. Consequently, attempts have been made to introduce various bacterial growth inhibitors, or deodorizing or antibacterial functional components into superabsorbent polymers.

[0006] However, in attempts to introduce antimicrobial agents that can inhibit bacterial growth into superabsorbent polymers, it is not easy to select and introduce antimicrobial agent components that exhibit excellent bacterial growth inhibition and deodorization properties, are harmless to humans and meet economic feasibility requirements, without deteriorating the basic physical properties of the superabsorbent polymer.

[0007] Therefore, there is a continued need to develop technologies related to superabsorbent polymers that can significantly inhibit bacterial growth without degrading the fundamental physical properties of the superabsorbent polymers. Summary of the Invention

[0008] Technical issues

[0009] Therefore, a superabsorbent polymer and a method for preparing the same are provided, wherein the superabsorbent polymer exhibits improved bacterial growth inhibition properties without degrading the absorption performance of the superabsorbent polymer.

[0010] Technical solution

[0011] According to an exemplary embodiment of the present invention,

[0012] A superabsorbent polymer is provided, comprising:

[0013] A base polymer comprising a crosslinked polymer obtained by polymerizing an acrylic acid-based monomer containing at least partially neutralized acidic groups, a polymerizable antimicrobial monomer represented by the following chemical formula 1, and a first crosslinking agent.

[0014] At least a portion of the base polymer is surface-treated with a second crosslinking agent:

[0015] [Chemical Formula 1]

[0016]

[0017] In chemical formula 1,

[0018] R1 to R3 are each independently hydrogen or methyl.

[0019] R4 is hydrogen or a substituted or unsubstituted alkyl group having 1 to 20 carbon atoms, and

[0020] L1 is a substituted or unsubstituted alkylene group having 1 to 10 carbon atoms.

[0021] According to another embodiment of the present invention,

[0022] A method for preparing superabsorbent polymers is provided, the method comprising the following steps:

[0023] Aqueous gel polymers are formed by crosslinking an acrylic-based monomer containing at least partially neutralized acidic groups with a polymerizable antimicrobial monomer represented by the following chemical formula 1 in the presence of a first crosslinking agent and a polymerization initiator.

[0024] A base polymer comprising a crosslinked polymer is formed by drying, pulverizing, and classifying an aqueous gel polymer; and

[0025] The surface of the base polymer is cross-linked by heat treatment in the presence of a second cross-linking agent.

[0026] [Chemical Formula 1]

[0027]

[0028] In chemical formula 1,

[0029] R1 to R3 are each independently hydrogen or methyl.

[0030] R4 is hydrogen or a substituted or unsubstituted alkyl group having 1 to 20 carbon atoms, and

[0031] L1 is a substituted or unsubstituted alkylene group having 1 to 10 carbon atoms.

[0032] Furthermore, according to yet another embodiment of the present invention, a hygiene product comprising the aforementioned superabsorbent polymer is provided.

[0033] Beneficial effects

[0034] The superabsorbent polymer of the present invention can exhibit antibacterial properties that inhibit the growth of bacteria that may be harmful to the human body and may cause secondary odors.

[0035] Specifically, since superabsorbent polymers are prepared by using polymerizable antimicrobial monomers with specific structures during the formation of cross-linked polymers, unlike superabsorbent polymers prepared by using other antimicrobial agents, they can exhibit antimicrobial properties against at least one Gram-negative bacterium while maintaining excellent water retention capacity, and the antimicrobial monomers used do not remain in the polymer, which will not cause safety issues in the human body due to leakage of antimicrobial agents.

[0036] Therefore, superabsorbent polymers are very suitable for various hygiene products that require antibacterial properties against bacteria, such as baby diapers and adult diapers. Detailed Implementation

[0037] The terminology used in this specification is for illustrative purposes only and is not intended to limit the invention. Singular expressions may include plural expressions unless the context otherwise allows. It must be understood that the terms “comprising / including,” “equipped with,” or “having” in this specification are used only to indicate the presence of an effective feature, step, component, or combination thereof, and do not preclude the presence or possibility of pre-added one or more different features, steps, components, or combinations thereof.

[0038] Furthermore, in this invention, when referring to layers or elements being formed "on" or "above" a layer or element, it means that each layer or element is formed directly on the layer or element, or that other layers or elements may be formed between layers, objects, or substrates.

[0039] This invention can be modified and has various forms, and specific exemplary embodiments are illustrated and described in detail in the following description. However, it is not intended to limit the invention to the specific exemplary embodiments, and it must be understood that the invention includes every modification, equivalent, or alternative included within the spirit and scope of the invention.

[0040] Furthermore, the technical terms used in this specification are for reference only to specific exemplary embodiments and are not intended to limit the invention. Unless the context otherwise allows, the singular expressions used herein may include the plural expressions.

[0041] At the same time, as used herein, the term "(meth)acrylate" includes both acrylate and methacrylate.

[0042] Furthermore, as used herein, the alkyl group can be linear or branched, and its carbon number is preferably from 1 to 20, but not particularly limited thereto. According to one embodiment, the alkyl group has 1 to 10 carbon atoms. According to another embodiment, the alkyl group has 1 to 6 carbon atoms. Specific examples of alkyl groups may include, but are not limited to, methyl, ethyl, propyl, n-propyl, isopropyl, butyl, n-butyl, isobutyl, tert-butyl, sec-butyl, 1-methyl-butyl, 1-ethyl-butyl, pentyl, n-pentyl, isopentyl, neopentyl, tert-pentyl, hexyl, n-hexyl, 1-methylpentyl, 2-methylpentyl, 4-methyl-2-pentyl, 3,3-dimethylbutyl, 2-ethylbutyl, heptyl, n-heptyl, 1-methylhexyl, cyclopentylmethyl, cyclohexylmethyl, octyl, n-octyl, tert-octyl, 1-methylheptyl, 2-ethylhexyl, 2-propylpentyl, n-nonyl, 2,2-dimethylheptyl, 1-ethyl-propyl, 1,1-dimethyl-propyl, isohexyl, 2-methylpentyl, 4-methylhexyl, 5-methylhexyl, etc. In this specification, the above description of alkyl groups can be applied to alkylene groups, except that alkylene groups are divalent groups.

[0043] As used herein, the term "polymer" refers to the polymerization state of an acrylic acid-based monomer and may encompass all ranges of water content or particle size. Among polymers, those having a water content of about 40% by weight or more after polymerization and before drying may be referred to as hydrated gel polymers, and particles obtained by pulverizing and drying hydrated gel polymers may be referred to as crosslinked polymers.

[0044] Furthermore, the term "superabsorbent polymer particles" refers to particulate materials containing a crosslinked polymer obtained by polymerizing and crosslinking an acrylic-based monomer containing at least partially neutralized acidic groups via a first crosslinking agent.

[0045] Furthermore, depending on the context, the term "superabsorbent polymer" refers to a crosslinked polymer obtained by polymerizing an acrylic acid-based monomer containing at least partially neutralized acidic groups, or a base polymer in powder form consisting of superabsorbent polymer particles obtained by pulverizing the crosslinked polymer, or a polymer suitable for commercial manufacturing by encompassing additional processes of the crosslinked polymer or base polymer, such as surface crosslinking, fine particle reorganization, drying, pulverization, grading, etc.

[0046] Traditionally, to ensure antibacterial and deodorizing properties in superabsorbent polymers, metal compounds with antibacterial functions or organic compounds containing cationic or alcohol functional groups are introduced as additives. However, this approach reduces the safety of the superabsorbent polymer, diminishes its fundamental physical properties such as absorption capacity, and presents problems with the durability of antibacterial properties and leakage of antibacterial substances.

[0047] For example, attempts have been made to introduce antimicrobial agents containing antimicrobial metal ions such as silver, copper, zinc, etc., into superabsorbent polymers. These antimicrobial metal ion-containing components can impart deodorizing properties by disrupting the cell walls of microorganisms such as bacteria and by killing bacteria possessing enzymes that may cause unpleasant odors in superabsorbent polymers. However, components containing metal ions are classified as antimicrobial materials that may kill even microorganisms beneficial to humans. Therefore, when superabsorbent polymers are used in hygiene products such as diapers for children or adults, the introduction of antimicrobial agents containing metal ions is avoided as much as possible.

[0048] Traditionally, when introducing antimicrobial agents that inhibit bacterial growth into superabsorbent polymers, the primary method is to mix the superabsorbent polymer with a small amount of the antimicrobial agent. However, when using this mixing method, it is difficult to maintain the antimicrobial growth properties uniformly over time. Furthermore, this mixing method can lead to the separation of the antimicrobial agent components and uneven coating characteristics during the mixing process, and also has disadvantages such as the need to install new mixing equipment.

[0049] Furthermore, various types of bacteria exist, with more than 5,000 types identified. Specifically, bacteria exhibit diverse cell morphologies such as spherical, rod-shaped, and spiral, and their oxygen requirements vary, thus leading to their classification as aerobic, facultative aerobic, and anaerobic bacteria. Consequently, a single type of antibacterial agent is unlikely to possess the physical / chemical mechanisms necessary to disrupt the cell membranes / cell walls or denature the proteins of many different bacteria.

[0050] However, it was discovered that when a superabsorbent polymer was prepared by polymerizing an acrylic acid-based monomer with a monomer containing a secondary amine with a specific structure, it exhibited absorption performance exceeding a predetermined level while simultaneously demonstrating antibacterial properties against at least one Gram-negative bacterium, thus completing the present invention. When the amino group of the polymerizable antibacterial monomer represented by Formula 1 combines with a positively charged proton, the interaction with the cell wall of the microorganism increases, and the alkyl group corresponding to the side group destabilizes the cell wall of the microorganism and inhibits its growth, thereby exhibiting antibacterial properties. Since most bacterial cell membranes are negatively charged, most antibacterial substances are positively charged. When a hydrogen cation (proton) combines with the amine of a compound represented by Formula 1 to exhibit cationic properties, it can interact with the bacterial cell membrane. Therefore, the compound represented by Formula 1 possesses antibacterial properties.

[0051] Furthermore, because the superabsorbent polymer contains antimicrobial monomers in the form of cross-linked polymers in which the antimicrobial monomers are cross-linked with acrylic acid-based monomers, the antimicrobial monomers do not remain in the superabsorbent polymer in the form of compounds. Therefore, there is no need to worry about leakage of antimicrobial agents even over time, thus the superabsorbent polymer is characterized by exhibiting excellent stability.

[0052] The superabsorbent polymer and its preparation method will be described in more detail below according to specific embodiments of the present invention.

[0053] Superabsorbent polymers

[0054] Specifically, the superabsorbent polymer according to one embodiment of the present invention is characterized in that,

[0055] The product comprises a base polymer comprising a crosslinked polymer obtained by polymerizing an acrylic acid-based monomer containing at least partially neutralized acidic groups, a polymerizable antimicrobial monomer represented by the following chemical formula 1, and a first crosslinking agent, wherein at least a portion of the base polymer is surface-treated with a second crosslinking agent.

[0056] [Chemical Formula 1]

[0057]

[0058] In chemical formula 1,

[0059] R1 to R3 are each independently hydrogen or methyl.

[0060] R4 is hydrogen or a substituted or unsubstituted alkyl group having 1 to 20 carbon atoms, and

[0061] L1 is a substituted or unsubstituted alkylene group having 1 to 10 carbon atoms.

[0062] In this respect, the crosslinked polymer produced by the crosslinking polymerization of an acrylic acid-based monomer and a polymerizable antimicrobial monomer in the presence of a first crosslinking agent has a three-dimensional network structure in which the main chain formed by the polymerization of the monomer is crosslinked by the first crosslinking agent. Therefore, the polymerizable antimicrobial monomer does not exist as a separate compound in the superabsorbent polymer, but rather as a repeating unit constituting the main chain, and thus does not leak over time. Therefore, the antimicrobial properties of the superabsorbent polymer can be maintained continuously.

[0063] In chemical formula 1, preferably, R1 and R2 are each hydrogen, and R3 can be methyl.

[0064] Furthermore, preferably, R4 can be a substituted or unsubstituted alkyl group having 1 to 10 carbon atoms, and more preferably, R4 can be tert-butyl. Generally, when the number of carbon atoms at the R4 position is higher, the affinity with the outer cell wall bilayer of microorganisms is higher, thus exhibiting strong antibacterial activity. In the case of alkyl groups having 8 or more carbon atoms, since they exhibit strong bactericidal properties even in water, having an appropriate length is important.

[0065] When the antimicrobial compound is terminal to a tertiary amine, it can function in terms of interaction with the microbial outer cell wall as described above. However, the electron-inducible effect is not increased, but the interaction between the cell membrane and the positively charged cell wall is negatively affected due to steric hindrance. In contrast, the compound represented by Formula 1 is terminal to a secondary amine, and in this case, the steric hindrance effect becomes smaller and it is more likely to bind to a proton to become positively charged, thus exhibiting a stronger interaction with the negatively charged cell wall of the microorganism. Therefore, even when R4 is a tert-butyl group with a relatively small number of carbon atoms, it can exhibit excellent antimicrobial properties.

[0066] Preferably, L1 can be a substituted or unsubstituted alkylene group having 1 to 5 carbon atoms, and more preferably, L1 can be an ethylene group.

[0067] For example, polymerizable antimicrobial monomers can be compounds represented by the following chemical formula 1-1:

[0068] [Chemical Formula 1-1]

[0069]

[0070] Meanwhile, the polymerizable antimicrobial monomer is included in the crosslinked polymer in an amount of 5 parts by weight or more and 20 parts by weight or less, relative to 100 parts by weight of the acrylic-based monomer. When the polymerizable antimicrobial monomer is included in an amount of less than 5 parts by weight relative to 100 parts by weight of the acrylic-based monomer, it is difficult to exhibit sufficient antimicrobial effect. When the polymerizable antimicrobial monomer is included in an amount of more than 20 parts by weight relative to 100 parts by weight of the acrylic-based monomer, the absorption performance of the superabsorbent polymer may deteriorate, and the polymerization rate of the superabsorbent polymer may decrease.

[0071] More specifically, the polymerizable antimicrobial monomer is included in the crosslinked polymer in amounts of 5 parts by weight or more, 5.5 parts by weight or more, or 6 parts by weight or more, and 20 parts by weight or less, 15 parts by weight or less, 12 parts by weight or less, 10 parts by weight or less, 9 parts by weight or less, or 8 parts by weight or less, relative to 100 parts by weight of the acrylic acid-based monomer. In this case, with regard to maintaining the absorption performance of the superabsorbent polymer (specifically, centrifugal retention capacity), the polymerizable antimicrobial monomer is included in the crosslinked polymer in amounts of 5 to 10 parts by weight relative to 100 parts by weight of the acrylic acid-based monomer.

[0072] In this respect, the polymerizable antimicrobial monomer is included in the crosslinked polymer in an amount of 5 to 20 parts by weight relative to 100 parts by weight of the acrylic acid-based monomer. This means that during the preparation of the crosslinked polymer, the polymerizable antimicrobial monomer is used in an amount of 5 to 20 parts by weight relative to 100 parts by weight of the acrylic acid-based monomer. This can be determined by whether the antimicrobial monomer is detected when examining the residual monomers of the superabsorbent polymer. In the superabsorbent polymer, no antimicrobial monomer was detected after preparation, which indicates that all the antimicrobial monomer used was consumed in the polymerization with the acrylic acid-based monomer.

[0073] For example, polymerizable antimicrobial monomers represented by chemical formula 1-1 exhibit antimicrobial properties against specific bacteria. Here, "exhibiting antimicrobial properties against specific bacteria" means that the number of bacteria cultured after absorbing artificial urine inoculated with test bacteria into a material without antimicrobial material is significantly reduced compared to the number of bacteria cultured after absorbing artificial urine inoculated with test bacteria into a reference material. Specifically, the antimicrobial properties are better because the bacterial growth inhibition rate calculated according to Equation 1 below, as described later in the antimicrobial property test, is higher.

[0074] [Equation 1]

[0075] Bacterial growth inhibition rate (%) = [(OD 参照 -OD 样品 ) / OD 参照 ]*100

[0076] In the equation, OD 参照 The absorbance and OD of the culture medium excluding antimicrobial materials are indicated. 样品 This indicates the absorbance of the culture medium containing antibacterial materials.

[0077] Alternatively, "exhibiting antibacterial properties against specific bacteria" means that the rate of reduction in bacterial inhibition (%) calculated by Equation 2 below is 45% or greater.

[0078] [Equation 2]

[0079] Antibacterial reduction rate (%) = (1-C) 样品 / C 参照 )*100

[0080] In the equation,

[0081] C 样品 This indicates the concentration (Co) of microorganisms in the culture medium containing the antimicrobial material.

[0082] C 参照 This indicates the concentration (Co) of microorganisms in the culture medium containing materials that do not contain antimicrobial materials.

[0083] More preferably, "exhibiting antibacterial properties against specific bacteria" means that the rate of reduction in bacterial inhibition (%) calculated by Equation 2 is 60% or greater, 70% or greater, 80% or greater, 90% or greater, 95% or greater, or 99% or greater.

[0084] Specifically, the polymerizable antimicrobial monomer represented by Formula 1-1 exhibits antimicrobial properties against Escherichia coli (E. coli) or Proteus mirabilis (P. mirabilis). The polymerizable antimicrobial monomer represented by Formula 1-1 exhibits antimicrobial properties against E. coli or Proteus mirabilis even when used in amounts of 3 parts by weight or greater and 7 parts by weight or less relative to 100 parts by weight of the superabsorbent polymer.

[0085] Meanwhile, the monomer based on acrylic acid is a compound represented by the following chemical formula 2:

[0086] [Chemical Formula 2]

[0087] R-COOM'

[0088] In chemical formula 2,

[0089] R is a hydrocarbon group containing unsaturated bonds and having 2 to 5 carbon atoms, and

[0090] M' can be a hydrogen atom, a monovalent or divalent metal, an ammonium group, or an organic amine salt.

[0091] Preferably, the monomer may include one or more of the following: (meth)acrylic acid and its monovalent (alkali) metal salt, its divalent metal salt, its ammonium salt, and its organic amine salt.

[0092] As described, when (meth)acrylic acid and / or its salts can be used as acrylic acid-based monomers, it is advantageous to obtain superabsorbent polymers with improved absorbency.

[0093] Here, the acrylic acid-based monomers may have at least partially neutralized acidic groups. Preferably, monomers partially neutralized by alkaline materials such as sodium hydroxide, potassium hydroxide, ammonium hydroxide, etc., can be used. In this regard, the degree of neutralization of the acrylic acid-based monomers can be 40 mol% to 95 mol%, or 40 mol% to 80 mol%, or 45 mol% to 75 mol%. The range of neutralization can be varied depending on the final physical properties. However, excessively high neutralization causes the neutralized monomers to precipitate, thus making polymerization difficult, while excessively low neutralization not only significantly degrades the absorbency of the polymer but also imparts unmanageable properties to the polymer, such as the properties of elastic rubber.

[0094] Furthermore, as used herein, the term "first crosslinking agent" is used to distinguish it from the second crosslinking agent, described later, which crosslinks the surface of the superabsorbent polymer particles, and serves to polymerize it by crosslinking the unsaturated bonds of the acrylic-based monomer and the polymerizable antimicrobial monomer. Whether surface crosslinking or internal crosslinking, the crosslinking in the above steps is performed. However, when the surface crosslinking process of the superabsorbent polymer particles, described later, is carried out, the surface of the ultimately prepared superabsorbent polymer particles has a crosslinked structure due to the second crosslinking agent, and its interior has a crosslinked structure due to the first crosslinking agent. Therefore, since the second crosslinking agent is primarily used for surface crosslinking of the superabsorbent polymer, it can be used as a surface crosslinking agent, and the first crosslinking agent, distinguished from the second crosslinking agent, can be used as an internal crosslinking agent.

[0095] Any compound can serve as the first crosslinking agent, as long as it can introduce crosslinking bonds during the polymerization of acrylic acid-based monomers. Non-limiting examples of the first crosslinking agent may include multifunctional crosslinking agents, such as N,N'-methylenebisacrylamide, trimethylolpropane tri(meth)acrylate, ethylene glycol di(meth)acrylate, polyethylene glycol (meth)acrylate, polyethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, polypropylene glycol (meth)acrylate, butanediol di(meth)acrylate, butanediol di(meth)acrylate, diethylene glycol di(meth)acrylate, hexanediol di(meth)acrylate, triethylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, dipentaerythritol pentaacrylate, glycerol tri(meth)acrylate, pentaerythritol tetraacrylate, triarylamine, ethylene glycol diglycidyl ether, propylene glycol, glycerol, or ethylene carbonate, which may be used alone or in combination of both or more thereof, but are not limited thereto.

[0096] Preferably, as the first crosslinking agent, a compound based on polyalkylene glycol di(meth)acrylate, such as polyethylene glycol (meth)acrylate, polyethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, or polypropylene glycol (meth)acrylate, can be used.

[0097] Crosslinking polymerization of acrylic acid monomers in the presence of a first crosslinking agent can be carried out by thermal polymerization, photopolymerization, or mixed polymerization in the presence of a polymerization initiator (as needed), a thickener, a plasticizer, a preservation stabilizer, an antioxidant, etc., and will be described in detail later.

[0098] Simultaneously, the superabsorbent polymer is further crosslinked via a second crosslinking agent, comprising a surface crosslinking layer formed on the crosslinked polymer. The surface crosslinking layer includes a surface treatment of at least a portion of the base polymer. This is to increase the surface crosslinking density of the superabsorbent polymer particles. As described, when the superabsorbent polymer particles also include a surface crosslinking layer, they can have a structure with an external crosslinking density higher than the internal crosslinking density.

[0099] As a second crosslinking agent, there are no particular limitations on using second crosslinking agents already used in the preparation of superabsorbent polymers. For example, the second crosslinking agent may include one or more polyols selected from ethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol, 1,2-hexanediol, 1,3-hexanediol, 2-methyl-1,3-propanediol, 2,5-hexanediol, 2-methyl-1,3-pentanediol, 2-methyl-2,4-pentanediol, tripropylene glycol, and glycerol; one or more carbonate-based compounds selected from ethylene carbonate, propylene carbonate, and glycerol carbonate; and epoxy compounds such as ethylene glycol diglycidyl ether, etc. Azoline compounds, for example Alzolidinediones, etc.; polyamine compounds; Azoline compounds; monozoline compounds 2-oxazolidinone, dioxazolidinone azole or polyoxinone Azoxyl ketone compounds; metal-containing sulfates such as aluminum sulfate or one or more polyvalent metal salts of carboxylates; or cyclic urea compounds; etc.

[0100] Specifically, one or more, two or more, or three or more of the above-mentioned second crosslinking agents can be used as the second crosslinking agent. For example, ethylene carbonate, propylene glycol, and / or aluminum sulfate can be used.

[0101] Furthermore, superabsorbent polymers can be in the form of particles with a particle size of 850 μm or smaller, for example, particles from about 150 μm to about 850 μm. In this regard, particle size can be measured according to the European Disposables and Nonwovens Association (EDANA) standard WSP 220.3 method. However, when a superabsorbent polymer contains a large number of fine particles smaller than 150 μm, it may degrade the general physical properties of the superabsorbent polymer, which is not preferred.

[0102] Furthermore, as mentioned above, the superabsorbent polymer can exhibit antibacterial properties against at least one Gram-negative bacterium. More specifically, the superabsorbent polymer can exhibit antibacterial properties against one or more bacteria classified as Gram-negative.

[0103] Gram-negative bacteria refer to bacteria that stain red when stained using the Gram staining method. Compared to Gram-positive bacteria, Gram-negative bacteria have an outer membrane composed of lipopolysaccharides, lipoproteins, and other complex polymeric materials, rather than a cell wall with a relatively small amount of peptidoglycan. Therefore, when Gram-negative bacteria are stained with a basic dye such as gentian violet and then treated with ethanol, they are decolorized; and when counterstained with a red dye such as safranin, they are stained red. Bacteria classified as Gram-negative include Proteus mirabilis, Escherichia coli, Salmonella typhi, Pseudomonas aeruginosa, and Vibrio cholerae, among others.

[0104] Because Gram-negative bacteria can cause a variety of diseases upon exposure and may also cause secondary infections in critically ill patients with weakened immune systems, it is preferable to use a single antimicrobial agent to achieve antimicrobial properties against one or more Gram-negative bacteria. In this regard, superabsorbent polymers can be effective against Gram-negative bacteria such as Escherichia coli or Proteus mirabilis, but are not limited to these.

[0105] Furthermore, as measured according to EDANA method WSP 241.3, superabsorbent polymers can exhibit a 30-minute centrifuge retention capacity (CRC) of 20 g / g or greater and 45 g / g or less for physiological saline (0.9 wt% sodium chloride aqueous solution). When the centrifuge retention capacity (CRC) is less than 20 g / g, the ability to retain liquid after absorption is reduced, therefore superabsorbent polymers are not suitable for use in hygiene products. More specifically, the centrifuge retention capacity (CRC) of superabsorbent polymers can be 20 g / g or greater, 25 g / g or greater, 30 g / g or greater, 35 g / g or greater, or 35.6 g / g or greater, and 45 g / g or less, 43 g / g or less, 41 g / g or less, 40 g / g or less, 38 g / g or less, or 37.4 g / g or less.

[0106] Therefore, the superabsorbent polymers described above, which contain a predetermined amount of polymerizable antimicrobial monomers in the crosslinked polymers, can have a centrifugal retention capacity (CRC) of 20 g / g to 45 g / g, while exhibiting excellent antimicrobial properties.

[0107] Methods for preparing superabsorbent polymers

[0108] Meanwhile, superabsorbent polymers can be prepared by the following method, which includes the following steps:

[0109] Aqueous gel polymers are formed by crosslinking an acrylic-based monomer containing at least partially neutralized acidic groups with a polymerizable antimicrobial monomer represented by Formula 1 in the presence of a first crosslinking agent and a polymerization initiator.

[0110] A base polymer comprising a crosslinked polymer is formed by drying, pulverizing, and classifying an aqueous gel polymer; and

[0111] The surface of the base polymer is cross-linked by heat treatment in the presence of a second cross-linking agent.

[0112] First, step 1 is a step of forming an aqueous gel polymer by crosslinking an acrylic-based monomer containing at least partially neutralized acidic groups with a polymerizable antimicrobial monomer in the presence of a first crosslinking agent and a polymerization initiator.

[0113] The steps may consist of a step of preparing a monomer composition by mixing an acrylic-based monomer, a first crosslinking agent, a polymerizable antimicrobial monomer, and a polymerization initiator, and a step of forming an aqueous gel polymer by performing thermal polymerization or photopolymerization of the monomer composition. In this regard, the descriptions of the acrylic-based monomer, the polymerizable antimicrobial monomer, and the first crosslinking agent can be referred to those described above.

[0114] In the monomer composition, a first crosslinking agent is included in an amount of 0.01 to 1 part by weight relative to 100 parts by weight of the acrylic-based monomer, thereby crosslinking the polymer. When the amount of the first crosslinking agent is less than 0.01 parts by weight, the improvement effect due to crosslinking is not significant. When the amount of the first crosslinking agent is greater than 1 part by weight, the absorbency of the superabsorbent polymer may decrease. More specifically, the first crosslinking agent may be included in an amount of 0.05 parts by weight or more, or 0.1 parts by weight or more, and 0.5 parts by weight or less, or 0.3 parts by weight or less, relative to 100 parts by weight of the acrylic-based monomer.

[0115] Furthermore, the polymerization initiator can be appropriately selected depending on the polymerization method. When using a thermal polymerization method, a thermal polymerization initiator is used. When using a photopolymerization method, a photopolymerization initiator is used. When using a mixed polymerization method (using both heat and light), both a thermal polymerization initiator and a photopolymerization initiator are used. However, even when using a photopolymerization method, a certain amount of heat is generated by light irradiation, such as UV irradiation, and a certain amount of heat is also generated during the polymerization reaction (which is exothermic). Therefore, a thermal polymerization initiator can also be used.

[0116] As a photopolymerization initiator, any compound capable of forming free radicals by light such as UV can be used without limitation, depending on its composition.

[0117] For example, one or more of the following can be used as photopolymerization initiators: benzoin ether, dialkyl acetophenone, hydroxyalkyl ketone, phenyl glyoxylate, benzyl dimethyl ketal, acylphosphine, and α-amino ketone. Specific examples of acylphosphine include diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide, phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide, and ethyl (2,4,6-trimethylbenzoyl)phenylphosphine sulfate. Many more different photopolymerization initiators are fully disclosed on page 115 of "UV Coatings: Basics, Recent Developments and New Application" by Reinhold Schwalm (Elsevier, 2007), and are not limited to the examples mentioned above.

[0118] The photopolymerization initiator may be included in an amount from 0.001 parts by weight to 1 part by weight relative to 100 parts by weight of the acrylic acid-based monomer. When the amount of photopolymerization initiator is less than 0.001 parts by weight, the polymerization rate may be slower, while when the amount of photopolymerization initiator is greater than 1 part by weight, the molecular weight of the superabsorbent polymer decreases and its physical properties may become inhomogeneous. More specifically, the photopolymerization initiator may be included in an amount of 0.005 parts by weight or more, or 0.01 parts by weight or more, or 0.1 parts by weight or more, and 0.5 parts by weight or less, or 0.3 parts by weight or less relative to 100 parts by weight of the acrylic acid-based monomer.

[0119] Furthermore, when a thermal polymerization initiator is also included as the polymerization initiator, one or more of the following can be used as the thermal polymerization initiator: persulfate-based initiators, azo-based initiators, hydrogen peroxide, and ascorbic acid. Specific examples of persulfate-based initiators may include sodium persulfate (Na2S2O8), potassium persulfate (K2S2O8), ammonium persulfate ((NH4)2S2O8), etc., and examples of azo-based initiators may include 2,2-azobis-(2-amidinylpropane) dihydrochloride, 2,2-azobis-(N,N-dimethylene)isobutyramidine dihydrochloride, 2-(carbamoylazo)isobutyronitrile, 2,2-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride, 4,4-azobis-(4-cyanopentanoic acid), etc. Many more different thermal polymerization initiators are fully disclosed on page 203 of "Principle of Polymerization" by Odian (Wiley, 1981); however, thermal polymerization initiators are not limited to the examples mentioned above.

[0120] The thermal polymerization initiator can be included in an amount from 0.001 parts by weight to 1 part by weight relative to 100 parts by weight of the acrylic-based monomer. When the amount of thermal polymerization initiator is less than 0.001 parts by weight, almost no further thermal polymerization occurs, and therefore the effect of adding the thermal polymerization initiator may be insignificant. When the amount of thermal polymerization initiator is greater than 1 part by weight, the molecular weight of the superabsorbent polymer may become lower and its physical properties may become non-uniform. More specifically, the thermal polymerization initiator can be included in an amount of 0.005 parts by weight or more, or 0.01 parts by weight or more, or 0.1 parts by weight or more, and 0.5 parts by weight or less, or 0.3 parts by weight or less relative to 100 parts by weight of the acrylic-based monomer.

[0121] In addition to polymerization initiators, one or more additives may be included during crosslinking polymerization as needed, such as surfactants, thickeners, plasticizers, preservation stabilizers, antioxidants, etc.

[0122] The monomer composition comprising an acrylic acid-based monomer, a polymerizable antimicrobial monomer, a first crosslinking agent, and optionally a photopolymerization initiator and additives may be in a solvent-soluble form.

[0123] As a suitable solvent, any solvent may be used without limitation, given the composition, as long as it can dissolve the above components. For example, a combination of one or more of the following may be used: water, ethanol, ethylene glycol, diethylene glycol, triethylene glycol, 1,4-butanediol, propylene glycol, ethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monomethyl ether acetate, methyl ethyl ketone, acetone, methyl pentyl ketone, cyclohexanone, cyclopentanone, diethylene glycol monomethyl ether, diethylene glycol ethyl ether, toluene, xylene, butyrolactone, carbitol, methyl cellosolve acetate, and N,N-dimethylacetamide. The solvent may be included in the remaining amount excluding the above components relative to the total amount of the monomer composition.

[0124] Furthermore, when using a water-soluble solvent such as water as the solvent and a terpene-based compound that is not soluble in water as the polymerizable antimicrobial monomer, a surfactant may be added in an amount of 10 parts by weight or less relative to 100 parts by weight of the polymerizable antimicrobial monomer to improve solubility.

[0125] Meanwhile, the method of forming aqueous gel polymers by thermal polymerization or photopolymerization of monomer compositions is not particularly limited in terms of composition, as long as it is a commonly used polymerization method.

[0126] Specifically, photopolymerization can be carried out by irradiating UV light with an intensity of 3mW to 30mW or 10mW to 20mW at temperatures of 60°C to 90°C, 70°C to 80°C, or 40°C to 50°C. When photopolymerization can be carried out under these conditions, cross-linked polymers can be formed with high polymerization efficiency.

[0127] Furthermore, when photopolymerization is carried out, it can be carried out in a reactor equipped with a movable conveyor belt or in a stainless steel container of a predetermined size. However, the above-described polymerization method is only one example, and the present invention is not limited to the above-described polymerization method.

[0128] Furthermore, as described above, when photopolymerization is carried out in a reactor equipped with a movable conveyor belt, the resulting aqueous gel polymer is typically a sheet-like aqueous gel polymer having the width of the belt. In this case, the thickness of the polymer sheet can be varied depending on the concentration and feed rate of the monomer composition fed therein. Generally, it is preferred to supply the monomer composition such that a sheet polymer with a thickness of about 0.5 cm to about 5 cm can be obtained. When the monomer composition is supplied to such an extent that the thickness of the sheet polymer becomes too thin, it is undesirable due to low production efficiency, while when the thickness of the sheet polymer is greater than 5 cm, the polymerization reaction may not occur uniformly across the entire thickness due to the excessive thickness.

[0129] Furthermore, the water content of the aqueous gel polymer obtained by the above method can be from about 40% to about 80% by weight relative to the total weight of the aqueous gel polymer. Meanwhile, as used herein, "water content" refers to the weight of water relative to the total weight of the aqueous gel polymer, and can be obtained by subtracting the weight of the dried polymer from the weight of the aqueous gel polymer. Specifically, the water content can be defined as a value calculated by measuring the weight loss due to the evaporation of moisture in the polymer during the drying process of raising the temperature of the polymer via infrared heating. In this case, the water content is measured under the following drying conditions: raising the temperature from room temperature to about 180°C, then maintaining the temperature at 180°C, and setting the total drying time to 20 minutes, including 5 minutes for the temperature raising step.

[0130] Meanwhile, after preparing the aqueous gel polymer, the prepared aqueous gel polymer can optionally be coarsely pulverized, followed by a subsequent drying and pulverizing process.

[0131] The coarse grinding process is used to improve drying efficiency and control the particle size of the prepared superabsorbent polymer powder during the subsequent drying process. In this regard, the pulverizer used herein is not limited in its construction, and specifically, it may include any of the following: vertical pulverizer, turbine cutter, turbine mill, rotary cutter mill, cutter mill, disc mill, shredder, crusher, meat grinder, and disc cutter, but is not limited to the examples described above.

[0132] The coarse grinding process can be carried out to, for example, reduce the particle size of the hydrated gel polymer to approximately 2 mm to approximately 10 mm. Due to the high water content of the hydrated gel polymer, grinding it to a particle size smaller than 2 mm is technically difficult and may result in particle agglomeration. Furthermore, when the hydrated gel polymer is ground to a particle size larger than 10 mm, the effect on improving the efficiency of the subsequent drying step may not be significant.

[0133] Next, step 2 is a step of forming a base polymer containing a crosslinked polymer by drying, pulverizing and classifying the aqueous gel polymer prepared in step 1.

[0134] The drying method can be chosen and used without limitation, as long as it is generally used in the drying of water-containing gel polymers. Specifically, the drying step can be carried out by methods such as hot air supply, infrared irradiation, microwave irradiation, ultraviolet irradiation, etc.

[0135] Specifically, drying can be carried out at a temperature of about 120°C to about 250°C. When the drying temperature is below 120°C, the drying time becomes too long and the physical properties of the resulting superabsorbent polymer may deteriorate. When the drying temperature is above 250°C, only the polymer surface is over-dried, which may result in fine particles during the subsequent pulverization process and may also deteriorate the physical properties of the resulting superabsorbent polymer. Therefore, drying can preferably be carried out at a temperature of 150°C or higher, or 160°C or higher, and 200°C or lower, or 180°C or lower.

[0136] Meanwhile, considering process efficiency, the drying time can be from about 20 minutes to about 90 minutes, but is not limited to this.

[0137] The water content of the polymer after such a drying step can be from about 5% by weight to about 10% by weight.

[0138] Following the drying process, a pulverizing process is performed. This pulverizing process can be carried out until the particle size of the polymer powder (i.e., the base polymer) is approximately 150 μm to approximately 850 μm. The pulverizer used for pulverizing to such a particle size can specifically include pin mills, hammer mills, spiral mills, roller mills, disc mills, jogging mills, etc., but the invention is not limited to the examples described above.

[0139] Following the above pulverization steps, in order to manage the physical properties of the superabsorbent polymer to be commercialized, the pulverized polymer powder can be further subjected to a classification process based on particle size.

[0140] The base polymer produced by the above process can be in the form of a fine powder comprising a crosslinked polymer obtained by crosslinking an acrylic-based monomer with a polymerizable antibacterial monomer via a first crosslinking agent. Specifically, the superabsorbent polymer can be in the form of a fine powder with a particle size of 150 μm to 850 μm or about 300 μm to about 600 μm.

[0141] Next, a step (step 3) may be included, in which the surface of the base polymer prepared in step 2 is cross-linked by heat treatment in the presence of a second cross-linking agent.

[0142] Surface crosslinking is a step that increases the crosslinking density near the surface of a superabsorbent polymer, in relation to the internal crosslinking density of the particles. Typically, a second crosslinking agent is applied to the surface of the polymer. Thus, the reaction occurs on the surface of the polymer particles, improving the crosslinking properties on the surface of the particles without significantly affecting the interior of the particles. Therefore, surface-crosslinked superabsorbent polymers have a higher level of crosslinking near the surface than in the interior.

[0143] The second crosslinking agent can be used in an amount from about 0.001 parts by weight to about 5 parts by weight relative to 100 parts by weight of the aqueous gel polymer. For example, the second crosslinking agent can be used in an amount from about 0.005 parts by weight or more, 0.01 parts by weight or more, or 0.05 parts by weight or more and 5 parts by weight or less, 4 parts by weight or less, or 3 parts by weight or less relative to 100 parts by weight of the superabsorbent polymer. Superabsorbent polymers exhibiting excellent general absorption properties can be prepared by controlling the amount of the second crosslinking agent within the above range.

[0144] Furthermore, the method of mixing the second crosslinking agent with the superabsorbent polymer is not limited by its composition. For example, methods such as feeding the second crosslinking agent and the superabsorbent polymer into a reactor and mixing them together, spraying the second crosslinking agent onto the superabsorbent polymer, or mixing them while continuously feeding the superabsorbent polymer and the second crosslinking agent into a continuously operating mixer can be used.

[0145] In addition to the second crosslinking agent, water and alcohol are mixed together, and these can be added in the form of a surface crosslinking solution. When water and alcohol are added, there is an advantage that the second crosslinking agent can be uniformly dispersed in the superabsorbent polymer powder. Here, for the purpose of inducing uniform dispersion of the second crosslinking agent, preventing agglomeration of the superabsorbent polymer powder, and simultaneously optimizing the surface penetration depth of the crosslinking agent, alcohol and water can be added in an amount of about 5 to about 12 parts by weight relative to 100 parts by weight of the polymer.

[0146] The surface crosslinking reaction can be carried out by heating the superabsorbent polymer powder, in which a second crosslinking agent has been added, at a temperature of about 80°C to about 220°C for about 15 minutes to about 100 minutes. When the crosslinking reaction temperature is below 80°C, sufficient surface crosslinking may not occur, while when the crosslinking reaction temperature is above 220°C, excessive surface crosslinking may occur. Furthermore, when the crosslinking reaction time is less than 15 minutes, sufficient crosslinking may not occur, while when the crosslinking reaction time exceeds 100 minutes, excessive surface crosslinking can lead to an excessive increase in the crosslinking density on the particle surface, resulting in deterioration of physical properties. More specifically, the surface crosslinking reaction can be carried out by heating at a temperature of 120°C or higher, or 140°C or higher and 200°C or lower, or 180°C or lower for 20 minutes or longer, or 40 minutes or longer and 70 minutes or less, or 60 minutes or less.

[0147] There are no particular limitations on the method used to raise the temperature of the additional crosslinking reaction. Heating can be carried out by providing a heating medium or by directly providing a heat source. In this regard, suitable types of heating media can be hot fluids such as steam, hot air, hot oil, etc. However, the invention is not limited to this. The temperature of the provided heating medium can be appropriately controlled by considering the type of heating medium, the heating rate, and the target temperature. Meanwhile, as a directly provided heat source, an electric heater or a gas heater can be used, but the invention is not limited to these examples.

[0148] In addition, hygiene products containing the aforementioned superabsorbent polymer are provided.

[0149] In the following description, for better understanding, the present invention will be presented in more detail. However, the following exemplary embodiments are merely illustrative of the invention, and the scope of the invention is not limited to the following exemplary embodiments.

[0150] [Example: Preparation of superabsorbent polymers]

[0151] Example 1

[0152] In a 3L glass container equipped with a stirrer, nitrogen feeder, and thermometer, 100 parts by weight of acrylic acid, 0.35 parts by weight of polyethylene glycol diacrylate (PEGDA, Mn=575) as the first crosslinking agent, 0.008 parts by weight of bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide as the photoinitiator, 0.12 parts by weight of sodium persulfate (SPS) as the thermal initiator, 123.5 parts by weight of a sodium hydroxide solution with a purity of 31.5%, 54.9 parts by weight of water, and 5 parts by weight of 2-(tert-butylamino)ethyl methacrylate (Sigma-Aldrich, product number 444332) were added to prepare an aqueous solution of a water-soluble unsaturated monomer while continuously feeding nitrogen.

[0153] An aqueous solution of the water-soluble unsaturated monomer was transferred to a stainless steel container with a width of 250 mm, a length of 250 mm, and a height of 30 mm, and then subjected to ultraviolet irradiation (dose: 10 mV / cm) in a UV chamber at 80 °C. 2 2 minutes and then mature for 2 minutes to obtain a water-containing gel polymer.

[0154] The obtained aqueous gel polymer was pulverized to a size of 3 mm x 3 mm, and then spread onto a stainless steel wire mesh with a pore size of 600 μm at a thickness of approximately 30 mm. The mesh was then dried in a hot air oven at 120°C for 11 hours. The resulting dried polymer was pulverized using a pulverizer and graded according to ASTM standards using standard sieves to obtain a base polymer with a particle size ranging from 150 μm to 850 μm.

[0155] Meanwhile, for surface crosslinking (an additional crosslinking) of the base polymer, a surface crosslinking solution was prepared based on 100 parts by weight of the base polymer by mixing 5.4 parts by weight of water, 1.2 parts by weight of ethylene carbonate, 0.2 parts by weight of propylene glycol, 0.2 parts by weight of polycarboxylic acid surfactant, and 0.2 parts by weight of aluminum sulfate. The surface crosslinking agent was sprayed onto 100 parts by weight of the base polymer using a paddle mixer at 1000 rpm. Then, surface crosslinking was performed by heat treatment at a maximum temperature of 184°C for 40 minutes to prepare the superabsorbent polymer of Example 1.

[0156] Example 2

[0157] The superabsorbent polymer was prepared in the same manner as in Example 1, except that in Example 1, 10 parts by weight of 2-(tert-butylamino)ethyl methacrylate was used and the surface crosslinking was carried out at a maximum temperature of 178°C for 30 minutes.

[0158] Comparative Example 1

[0159] The superabsorbent polymer was prepared in the same manner as in Example 1, except that 2-(tert-butylamino)ethyl methacrylate was not used in Example 1.

[0160] Comparative Example 2

[0161] 18.5 g of 2-(tert-butylamino)ethyl methacrylate and 30 mL of ethanol were added to a two-necked round-bottom flask capable of maintaining a nitrogen atmosphere, and the mixture was stirred for 10 minutes. Subsequently, azobisisobutyronitrile (AIBN (493 mg)) was added, and the mixture was stirred at 80 °C for 16 hours. The reaction mixture was cooled to room temperature, and a small amount of ethanol was added to dilute the solution. The diluted solution was slowly added dropwise to distilled water. The resulting solid was filtered, washed with a small amount of distilled water, and dried to obtain the 2-(tert-butylamino)ethyl methacrylate polymer (Mw = 32856, Mn = 21055, Mp = 49340, PD = 1.6).

[0162] A superabsorbent polymer mixture was prepared by mixing 5 parts by weight of 2-(tert-butylamino)ethyl methacrylate polymer with 100 parts by weight of a superabsorbent polymer prepared in the same manner as in Comparative Example 1.

[0163] Comparative Example 3

[0164] 18.5 g of 2-(tert-butylamino)ethyl methacrylate and 30 mL of ethanol were added to a two-necked round-bottom flask capable of maintaining a nitrogen atmosphere, and the mixture was stirred for 10 minutes. Subsequently, azobisisobutyronitrile (AIBN (493 mg)) was added, and the mixture was stirred at 80 °C for 16 hours. The reaction mixture was cooled to room temperature, and a small amount of ethanol was added to dilute the solution. The diluted solution was slowly added dropwise to distilled water. The resulting solid was filtered, washed with a small amount of distilled water, and dried to obtain the 2-(tert-butylamino)ethyl methacrylate polymer (Mw = 32856, Mn = 21055, Mp = 49340, PD = 1.6).

[0165] A superabsorbent polymer mixture was prepared by mixing 10 parts by weight of 2-(tert-butylamino)ethyl methacrylate polymer with 100 parts by weight of a superabsorbent polymer prepared in the same manner as in Comparative Example 1.

[0166] The Mw, Mn, Mp, and PD of the 2-(tert-butylamino)ethyl methacrylate polymers of Comparative Examples 2 and 3 were measured using the following method. The molecular weight distribution (PD = Mw / Mn) was determined by measuring Mw and Mn using gel permeation chromatography (GPC). This test was performed using a Waters E2695,2414RI instrument from Polymer Laboratories with a PLgel MIX-C / D 300 mm column. The test temperature was 40 °C, N,N-dimethylformamide (DMF) was used as the solvent, and the test was performed at a flow rate of 1 mL / min. Samples were prepared at a concentration of 5 mg / 1 mL and then supplied in 100 μL increments. The values ​​of Mw and Mn were obtained using a calibration curve formed using polymethyl methacrylate (PMMA) standards. Nine polymethyl methacrylate (PMMA) standards with molecular weights of 1,980 / 13,630 / 32,340 / 72,800 / 156,200 / 273,600 / 538,500 / 1,020,000 / 1,591,000 were used.

[0167] [Experimental Example]

[0168] (1) Evaluation of the antimicrobial properties of polymerizable antimicrobial monomers against Escherichia coli

[0169] The antibacterial properties of the monomers 2-(tert-butylamino)ethyl methacrylate and 2-(dimethylamino)ethyl methacrylate included in the examples were evaluated using the following methods.

[0170] The antibacterial properties of 2-(tert-butylamino)ethyl methacrylate are shown in Experimental Examples 1-1 to 1-3, and the antibacterial properties of 2-(dimethylamino)ethyl methacrylate are shown in Comparative Experimental Examples 1-2 to 1-4.

[0171]

[0172] According to the concentrations specified in Table 1 below, monomers were placed into 50 ml conical tubes, and then 25 ml of nutrient broth (Becton Dickinson) solution inoculated with a standard strain of *E. coli* (ATCC 25922) at 3000 ± 300 CFU / ml was injected. After incubation for 18 hours in a shaking incubator (Vision Scientific, VS-37SIF) at 35°C, the culture solution was diluted to 1 / 5 concentration using 1X PBS (Gibco). The absorbance of the diluted solution was measured at 600 nm using a UV-Vis spectrophotometer. The absorbance of the nutrient broth solution inoculated with bacteria without monomer was then compared with that of the sample containing monomer to examine the degree of bacterial growth. The bacterial growth inhibition rate was calculated according to Equation 1 below, and the results are shown in Table 1.

[0173] [Equation 1]

[0174] Bacterial growth inhibition rate (%) = [(OD 参照 -OD 样品 ) / OD 参照 ]*100

[0175] In the equation, OD 参照 The absorbance and OD of the culture medium in Comparative Experiment Example 1-1, which does not contain antibacterial materials, are shown. 样品 This indicates the absorbance of the culture medium containing antibacterial materials.

[0176] [Table 1]

[0177]

[0178] According to Table 1, when the polymerizable antimicrobial monomer of the present invention is included, the bacterial growth inhibition rate is better than that of the case in which the same amount of different monomers of comparative experimental examples, 2-(dimethylamino)ethyl methacrylate (with a tertiary amine substituent), are used.

[0179] (2) Evaluation of the antimicrobial properties of polymerizable antimicrobial monomers against Proteus mirabilis (P. mirabilis)

[0180] To examine the antimicrobial properties of the monomers 2-(tert-butylamino)ethyl methacrylate and 2-(dimethylamino)ethyl methacrylate included in the examples against *Proteus mirabilis*, the bacterial growth inhibition rate (%) against *Proteus mirabilis* was calculated in the same manner as in the evaluation of its antimicrobial properties against *Escherichia coli*, except that a nutrient broth solution inoculated with a standard strain of *Proteus mirabilis* (ATCC 29906) at a concentration of 3000 ± 300 CFU / ml was used instead of *Escherichia coli* (ATCC 25922). The results are shown in Table 2 below.

[0181] When calculating the bacterial growth inhibition rate using Equation 1, C 参照 The CFU of bacteria after culturing with the monomer of Comparative Experiment Example 2-1, which does not contain antimicrobial material.

[0182] [Table 2]

[0183]

[0184] According to Table 2, when the polymerizable antimicrobial monomer of the present invention is included, the bacterial growth inhibition rate is better than that of the case in which the same amount of the different monomers 2-(dimethylamino)ethyl methacrylate (with a tertiary amine group at the end) of the comparative experimental examples are used.

[0185] (3) Evaluation of the absorption properties of superabsorbent polymers

[0186] The centrifugal retention capacity (CRC) of the superabsorbent polymers of the examples and comparative examples was evaluated using the following methods, and is shown in Table 3.

[0187] According to the European Disposable Products and Nonwovens Association (EDANA) standard WSP 241.3, the centrifugal retention capacity of the superabsorbent polymers and base polymers of the Examples and Comparative Examples under no-load conditions was measured.

[0188] In detail, after uniformly introducing W0(g) (approximately 0.2g) of the superabsorbent polymer into a bag made of nonwoven fabric and sealing it, the bag was immersed in physiological saline (0.9 wt% sodium chloride aqueous solution) at room temperature. After 30 minutes, the bag was drained for 3 minutes using a centrifuge at 250G, and then the weight of the bag W2(g) was measured. Furthermore, after performing the same operation without using the polymer, the weight of the bag W1(g) was measured. CRC (g / g) was calculated using the obtained weights according to the following equation:

[0189] [Equation 3]

[0190] CRC(g / g)={[W2(g)-W1(g)] / W0(g)}-1

[0191] In equation 3,

[0192] W0(g) is the initial weight (g) of the superabsorbent polymer.

[0193] W1(g) is the weight of the bag after it has been immersed in physiological saline for 30 minutes and then drained at 250g for 3 minutes using a centrifuge.

[0194] W2(g) is the weight of the bag containing the superabsorbent polymer, measured after the superabsorbent polymer has been soaked in physiological saline at room temperature for 30 minutes and then drained at 250g for 3 minutes using a centrifuge.

[0195] (4) Evaluation of the antibacterial properties of superabsorbent polymers against Escherichia coli (E. coli)

[0196] Two g of each of the superabsorbent polymers prepared in the examples and comparative examples were placed in a 250 ml cell culture flask, and 50 ml of artificial urine inoculated with standard beads of the test bacterium *Escherichia coli* (ATCC 25922) at a concentration of 3000 ± 300 CFU / ml was injected into the flask. The flask was then mixed for approximately 1 minute to allow the superabsorbent polymer to fully absorb the artificial urine solution. When the polymer had fully absorbed the solution, it exhibited a gel form and was incubated at 35°C (JEIO TECH) for 12 hours. For samples that had completed their incubation, 150 ml of 0.9 wt% NaCl solution was added, followed by shaking for approximately 1 minute. This dilution was then spread onto an agar plate. Colony counting was subsequently performed on the serial dilutions, using 0.9 wt% NaCl solution in this step. The antimicrobial performance was determined by calculating the initial bacterial concentration (Co, CFU / ml) based on the dilution concentration, and then calculating the inhibition rate (%) against *Escherichia coli* (ATCC 25922) according to Equation 2 below. The results are shown in Table 3 below.

[0197] [Equation 2]

[0198] Antibacterial reduction rate (%) = (1-C) 样品 / C 参照 )*100

[0199] When calculating the antibacterial reduction rate using Equation 2, C 样品 This refers to the CFU of bacteria cultured after culturing superabsorbent polymers containing antimicrobial materials, and C... 参照 The CFU of bacteria after culturing the superabsorbent polymer of Comparative Example 1, which does not contain antimicrobial material.

[0200] (5) Evaluation of the antibacterial properties of superabsorbent polymers against Proteus mirabilis (P. mirabilis)

[0201] To examine the antimicrobial properties of the superabsorbent polymers prepared in the Examples and Comparative Examples against *Proteus mirabilis*, the inhibition rate (%) against *Proteus mirabilis* was calculated in the same manner as in '(4) Evaluation of the antimicrobial properties of the superabsorbent polymers against *Escherichia coli*,' except that *Proteus mirabilis* was used instead of the standard strain of *Escherichia coli* (ATCC 25922). The results are shown in Table 3 below.

[0202] (6) Evaluation of ammonia deodorization

[0203] The deodorization properties of the superabsorbent polymers in the examples and comparative examples were evaluated using the following methods.

[0204] In detail, the superabsorbent polymers prepared in the Examples and Comparative Examples were injected at a concentration of 0.04 g / ml per 1 ml of solvent into 50 ml of artificial urine inoculated with Proteus mirabilis (ATCC 29906) at 10,000 CFU / ml, and then incubated at 35°C (JEIO TECH) for 12 hours. After connecting the ammonia detection tube (Gastech, Ammonia 3M) and a suitable pump (Gastech, GV-100) to the culture container, 50 ml was extracted using a syringe needle. The ammonia changed the color of the detection tube, and the scale was checked and compared. The composition of the artificial urine used here was prepared using the method described in J Wound Ostomy Continence Nurs. 2017; 44(1) 78-83. The results are shown in Table 3 below.

[0205] [Table 3]

[0206] Example 1 Example 2 Comparative Example 1 Comparative Example 2 Comparative Example 3 CRC (g / g) of the basic polymer 43.7 40.4 44.6 43.7 43.7 CRC (g / g) of the final superabsorbent polymer 35.6 37.4 36.7 35.6 35.6 Surface crosslinking time (minutes) 40 30 40 40 40 Surface crosslinking temperature (°C) 184 178 184 184 184 Inhibition rate (%) against Escherichia coli 47.05 95.49 - 0 4.05 Inhibition rate (%) against Proteus mirabilis 87.85 99.99 - 0 9.40 Ammonia (ppm) <10 <10 >500 >500 >500

[0207] The results in Table 3 show that, by controlling the surface crosslinking time and temperature, the superabsorbent polymers of Examples 1 and 2, as well as Comparative Example 1, exhibited equivalent levels of CRC, while demonstrating high inhibition reduction rates against *Escherichia coli* and *Proteus mirabilis*, thus indicating antibacterial properties. In Comparative Examples 2 and 3, the superabsorbent polymer of Example 1 was used, therefore they possessed the same absorption characteristics as those of Example 1. However, it was determined that simply mixing the polymers significantly reduced the antibacterial properties against *Escherichia coli* and *Proteus mirabilis*.

[0208] Furthermore, *Proteus mirabilis* (a microorganism possessing enzymes such as urease) breaks down urea contained in artificial urine into ammonia. Therefore, as *Proteus mirabilis* proliferates, the amount of ammonia increases, thus significantly increasing the odor of the urine. As shown in Table 3, ammonia production was significantly reduced in the examples compared to the comparative examples, demonstrating excellent deodorizing effects due to antibacterial action.

Claims

1. A superabsorbent polymer comprising a base polymer, said base polymer comprising a crosslinked polymer obtained by polymerizing an acrylic acid-based monomer comprising at least partially neutralized acidic groups, a polymerizable antimicrobial monomer represented by the following chemical formula 1, and a first crosslinking agent. At least a portion of the base polymer is surface-treated with a second crosslinking agent: [Chemical Formula 1] In chemical formula 1, R1 to R3 are each independently hydrogen or methyl. R4 is hydrogen or a substituted or unsubstituted alkyl group having 1 to 20 carbon atoms, and L1 is a substituted or unsubstituted alkylene group having 1 to 10 carbon atoms.

2. The superabsorbent polymer according to claim 1, R1 and R2 are each hydrogen, and R3 is methyl.

3. The superabsorbent polymer according to claim 1, R4 is tert-butyl.

4. The superabsorbent polymer according to claim 1, L1 is ethylene.

5. The superabsorbent polymer according to claim 1, The polymerizable antibacterial monomer is a compound represented by the following chemical formula 1-1: [Chemical Formula 1-1] 6. The superabsorbent polymer according to claim 1, The polymerizable antimicrobial monomer is used in amounts of 5 parts by weight or more and 20 parts by weight or less, relative to 100 parts by weight of the acrylic-based monomer.

7. The superabsorbent polymer according to claim 1, The superabsorbent polymer exhibits antibacterial properties against Gram-negative bacteria.

8. The superabsorbent polymer according to claim 7, The Gram-negative bacteria mentioned therein are Escherichia coli or Proteus mirabilis.

9. The superabsorbent polymer according to claim 1, The superabsorbent polymer exhibits a 30-minute centrifugation retention capacity (CRC) of 20 g / g or greater and 45 g / g or less for physiological saline solution of 0.9 wt% sodium chloride aqueous solution, as measured according to EDANA method WSP 241.

3.

10. A method for preparing a superabsorbent polymer, the method comprising the following steps: Aqueous gel polymers are formed by crosslinking an acrylic-based monomer containing at least partially neutralized acidic groups with a polymerizable antimicrobial monomer represented by the following chemical formula 1 in the presence of a first crosslinking agent and a polymerization initiator. A base polymer comprising a crosslinked polymer is formed by drying, pulverizing, and classifying the aqueous gel polymer; and The surface of the base polymer is crosslinked by heat treatment in the presence of a second crosslinking agent. [Chemical Formula 1] In chemical formula 1, R1 to R3 are each independently hydrogen or methyl. R4 is hydrogen or a substituted or unsubstituted alkyl group having 1 to 20 carbon atoms, and L1 is a substituted or unsubstituted alkylene group having 1 to 10 carbon atoms.

11. The method for preparing superabsorbent polymer according to claim 10, The polymerizable antimicrobial monomer is used in amounts of 5 parts by weight or more and 20 parts by weight or less, relative to 100 parts by weight of the acrylic-based monomer.

12. A hygiene product comprising the superabsorbent polymer according to any one of claims 1 to 9.

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