Biodegradable highly absorbent resin and its manufacturing method

Abstract

The present invention provides a highly water-absorbent resin that exhibits excellent biodegradability without reducing the physical properties of the highly water-absorbent resin, such as water retention capacity and absorbency under pressure, and a method for producing the same.

Description

[Technical Field]

[0001] Cross-citation of related applications (etc.) This application claims the benefit of priority based on Korean Patent Application No. 10-2021-0090425, filed July 9, 2021, and Korean Patent Application No. 10-2022-0079572, filed June 29, 2022, and all contents disclosed in the documents of said Korean patent applications are incorporated herein by reference.

[0002] The present invention relates to a biodegradable superabsorbent polymer that exhibits excellent biodegradability without reducing the physical properties of the superabsorbent polymer, such as water retention capacity and absorbency under pressure, and a method for producing the same. [Background technology]

[0003] Super absorbent polymers (SAPs) are synthetic polymers capable of absorbing 500 to 1,000 times their own weight in water, and are given different names by different developers, such as SAM (Super Absorbency Material) or AGM (Absorbent Gel Material). These super absorbent polymers first came into practical use as sanitary products, and are now widely used in a variety of applications, including sanitary products such as baby diapers, soil water retention agents in gardening, water-stopping materials in civil engineering and construction, seedling sheets, freshness-preserving agents in the food distribution industry, and materials for poultices, as well as electrical insulation.

[0004] Such superabsorbent polymers are typically manufactured by bulk polymerization or suspension polymerization of acrylic acid-based monomers with a crosslinking agent in the presence of a polymerization initiator to obtain a crosslinked polymer. Therefore, conventional superabsorbent polymers are rarely biodegradable, causing environmental problems when disposed of as waste. Specifically, when various products containing superabsorbent polymers are buried and discarded, the superabsorbent polymers are not decomposed by bacteria and microorganisms in the soil, which can cause environmental pollution.

[0005] Therefore, attempts have been made to develop superabsorbent polymers that exhibit excellent biodegradability using biomass-derived materials, but it has not been so easy to produce economically producible biodegradable superabsorbent polymers that exhibit similar levels of physical properties to conventional superabsorbent polymers.

[0006] As a result, there is a continuing demand for the development of technologies related to superabsorbent polymers that can exhibit biodegradability without deteriorating the basic physical properties of the superabsorbent polymers. Summary of the Invention [Problem to be solved by the invention]

[0007] Therefore, the present invention provides a highly water-absorbent resin that exhibits excellent biodegradability without reducing the physical properties of the highly water-absorbent resin, such as water retention capacity and absorbency under pressure, and a method for producing the same. [Means for solving the problem]

[0008] According to one embodiment of the present invention, a base resin comprising a crosslinked polymer of an unmodified or acid group-containing modified polysaccharide and a first crosslinker; a biodegradable highly absorbent resin in which at least a portion of the base resin is crosslinked by a second crosslinking agent, the first cross-linking agent comprises a cyclic carboxylic acid anhydride; the second crosslinking agent includes an epoxy compound; A biodegradable superabsorbent polymer is provided.

[0009] According to another embodiment of the present invention, Step 1: crosslinking an unmodified or acid group-containing modified polysaccharide in the presence of a first crosslinking agent to produce a crosslinked polymer; Step 2: Drying and grinding the crosslinked polymer to produce a base resin; and (Step 3) crosslinking at least a portion of the base resin in the presence of a second crosslinker, the first cross-linking agent comprises a cyclic carboxylic acid anhydride; the second crosslinking agent includes an epoxy compound; A method for producing a biodegradable superabsorbent polymer is provided.

[0010] Furthermore, according to yet another embodiment of the present invention, there is provided an article comprising the biodegradable superabsorbent polymer. [Effects of the Invention]

[0011] The biodegradable superabsorbent resin of the present invention exhibits excellent biodegradability because it contains a crosslinked polymer in which polysaccharides are crosslinked with a crosslinking agent, and the crosslinked polymer further contains a crosslinked layer in which at least a portion of the crosslinked polymer is crosslinked with a second crosslinking agent, so that the physical properties of general superabsorbent resins, such as water retention capacity and pressure absorption capacity, are not impaired.

[0012] Therefore, the biodegradable highly water-absorbent resin can be applied to a variety of sanitary products, and does not cause environmental pollution problems when disposed of. DETAILED DESCRIPTION OF THE INVENTION

[0013] The terms used in this specification are merely used to describe exemplary embodiments and are not intended to limit the invention. The singular expressions include the plural expressions unless the context clearly dictates otherwise. In this specification, the terms "comprise," "comprise," "have," and the like are intended to specify the presence of implemented features, steps, components, or combinations thereof, and should be understood as not precluding the presence or additional possibility of one or more other features, steps, components, or combinations thereof.

[0014] Furthermore, in the present invention, when a layer or element is referred to as being formed "on" or "on" another layer or element, it means that the layer or element is formed directly on the other layer or element, or that other layers or elements can be additionally formed between the layers, on the object, or on the substrate.

[0015] The present invention can be modified in various ways and can have various forms, so that specific embodiments are illustrated and described in detail below, but it is not intended to limit the present invention to the specific disclosed embodiments, and it should be understood that the present invention includes all modifications, equivalents, and alternatives included within the spirit and technical scope of the present invention.

[0016] Furthermore, the terminology used herein is merely for the purpose of referring to particular embodiments and is not intended to limit the present invention, and the singular forms used herein also include the plural forms unless the context clearly dictates otherwise.

[0017] On the other hand, the term "(meth)acrylate" as used herein includes both acrylate and methacrylate.

[0018] The term "crosslinked polymer" as used in the present specification means that a plurality of polysaccharides are crosslinked with a crosslinking agent to form a polymerized state, and can encompass any range of moisture content or particle size.

[0019] Furthermore, depending on the context, the term "superabsorbent polymer" may refer to a crosslinked polymer in which multiple polysaccharides are crosslinked and polymerized with a crosslinking agent, or a powder-like base resin consisting of superabsorbent polymer particles obtained by pulverizing the crosslinked polymer, or may refer to any of the crosslinked polymers or base resins that have been subjected to additional processes, such as additional crosslinking, pulverization into fine powder, drying, pulverization, classification, etc., to be in a state suitable for commercialization.

[0020] The term "superabsorbent resin particles" refers to a particulate material obtained by pulverizing a superabsorbent resin.

[0021] Conventionally used superabsorbent resins have acidic groups, and at least a portion of the acidic groups are produced by polymerizing an acrylic acid-based monomer together with a crosslinking agent in the presence of a polymerization initiator. However, superabsorbent resins produced in this manner are not biodegradable, causing environmental problems.

[0022] Therefore, in order to develop a biodegradable superabsorbent resin, methods such as copolymerizing acrylic acid monomers with biodegradable materials such as polysaccharide, polyaspartic acid, and polyglutamic acid to produce a superabsorbent resin have been discussed. However, there has been a problem in that the balance between water retention capacity and pressure absorption capacity, which are important physical properties of a superabsorbent resin, is reduced.

[0023] Therefore, the present inventors have confirmed that when a highly absorbent resin is produced by crosslinking a polysaccharide with a cyclic carboxylic acid anhydride and then further crosslinking this with an epoxy compound, not only is it highly biodegradable but it also has a better balance of water retention capacity and absorbency under pressure than previously known biodegradable materials, and have thus completed the present invention.

[0024] Hereinafter, the biodegradable highly water-absorbent polymer and its manufacturing method will be described in more detail with reference to specific embodiments of the present invention.

[0025] Biodegradable super absorbent resin According to one embodiment, the biodegradable superabsorbent resin comprises a base resin including a first crosslinked polymer of an unmodified or acidic group-containing modified polysaccharide and a first crosslinker, and the base resin is at least partially crosslinked by a second crosslinker, wherein the first crosslinker includes a cyclic carboxylic acid anhydride and the second crosslinker includes an epoxy compound.

[0026] First, the biodegradable superabsorbent resin includes a base resin containing a cross-linked polymer of a polysaccharide and a first cross-linking agent, and the base resin is generally in the form of a powder made of resin particles.

[0027] Here, polysaccharides, i.e., polysaccharides, refer not only to polymeric carbohydrate molecules consisting of glucose units, but also to polymeric carbohydrate molecules consisting of glucosamine units in which an amino group has been introduced to the hydroxy group bonded to the carbon atom C2 at position 2 in a glucose unit, and / or N-acetylglucosamine units in which an N-acetylamino group has been introduced to the hydroxy group bonded to the carbon atom C2 at position 2 in a glucose unit.

[0028] Therefore, the term "polysaccharide" as used herein can be understood as a comprehensive concept of all compounds generally known as polysaccharides. Examples of polysaccharides include, but are not limited to, starch composed of repeating glucose units, dextrin, which is a hydrolyzate of such starch, and chitosan composed of repeating glucosamine and N-acetylglucosamine units.

[0029] More specifically, the polysaccharide may be one or more selected from the group consisting of starch, dextrin, and chitosan.

[0030] The polysaccharide constituting the crosslinked polymer of the biodegradable highly water-absorbent resin may be a non-modified polysaccharide or a modified polysaccharide containing an acidic group.

[0031] Specifically, unmodified polysaccharides are distinguished from modified polysaccharides, which are polysaccharides in which the hydroxyl groups (-OH) in the glycose repeating units that make up the polysaccharide have been replaced with other functional groups by chemical and / or heat treatment. Superabsorbent resins containing crosslinked polymers made from such unmodified polysaccharides have the advantage of reducing the number of process steps and the amount of raw material required, thereby reducing costs during mass production, compared to superabsorbent resins containing crosslinked polymers made from modified polysaccharides made from polysaccharides substituted with other functional groups such as carboxyl groups.

[0032] In addition, the acidic group-containing modified polysaccharide is a modified polysaccharide, which, unlike the non-modified polysaccharide, has a structure in which at least one hydroxy group (-OH) in the glycose repeating unit constituting the polysaccharide is substituted with an acidic group by chemical and / or heat treatment.

[0033] The degree of substitution (DS) of the acidic group in the acidic group-containing modified polysaccharide may be 0.1 to 0.99. If the degree of substitution is too low, a large amount of modified polysaccharide may remain that does not participate in the cross-linking polymerization, while if the degree of substitution is too high, the physical properties of the final superabsorbent resin may be affected. For example, the degree of substitution (DS) of the acidic group in the acidic group-containing modified polysaccharide may be 0.4 or more, 0.5 or more, 0.6 or more, or 0.7 or more, and 0.9 or less, 0.8 or less, or 0.75 or less.

[0034] Here, the degree of substitution of acidic groups refers to the average number of hydroxyl groups (-OH) substituted with acidic groups per glycose repeating unit. In other words, since there are three hydroxyl groups per glycose repeating unit, the theoretical maximum degree of substitution is 3, and a degree of substitution of 0.1 means that one hydroxyl group is substituted per 10 glycose repeating units. In addition, such a degree of substitution of acidic groups is determined by the average number of hydroxyl groups (-OH) substituted with acidic groups per glycose repeating unit. 1 It can be calculated through H NMR analysis.

[0035] On the other hand, when the acidic group-containing modified polysaccharide contains a carboxyl group, such a carboxyl group-containing modified polysaccharide may be prepared by reacting the hydroxyl group of a non-modified polysaccharide with a carboxylic acid or its salt, such as sodium chloroacetate, succinic acid, or itaconic acid.

[0036] In this case, the acidic groups in the acidic group-containing modified polysaccharide may be carboxyl groups, and at least a portion of the carboxyl groups may be neutralized. The degree of neutralization of the acidic groups in the modified polysaccharide may be adjusted depending on the type of modified polysaccharide and the properties of the final superabsorbent resin to be realized. For example, in the case of a polysaccharide that is insoluble in water due to its high molecular weight, the carboxyl groups (COOH) may be converted to carboxylates (COO - ) form, the degree of neutralization can be increased to increase the solubility in water. Specifically, the degree of neutralization of the modified polysaccharide may be 40 to 95 mol%, or 40 to 80 mol%, or 45 to 75 mol%.

[0037] For example, the acidic group-containing modified polysaccharide may be prepared by reacting an unmodified polysaccharide with hydroxide and sodium chloroacetate. The acidic group-containing modified polysaccharide produced by such a reaction is a carboxymethylated polysaccharide. Here, carboxymethylation can occur at the hydroxy group at the carbon C2 at the 2nd position, the carbon C3 at the 3rd position, or the carbon C6 at the 6th position in the anhydroglycose unit (AGU) represented by the following chemical formula A. That is, the carboxymethylated polysaccharide is prepared by converting one or more hydroxy groups (OH) in the anhydroglycose unit (AGU) to a carboxymethyl group (OCH2COOH / OCH2COO - ) has a structure substituted with.

[0038] The polysaccharide may have a weight-average molecular weight of 10,000 to 4,000,000 g / mol. If the weight-average molecular weight of the polysaccharide is too low, it may be difficult to form a crosslinked polymer exhibiting a certain level of strength, whereas if the weight-average molecular weight of the polysaccharide is too high, the reaction with the first crosslinker may be difficult due to entanglement of the polymer chains of the high molecular weight polysaccharide, resulting in insufficient crosslinking.

[0039] Here, the weight-average molecular weight (Mw) can be measured using gel permeation chromatography (GPC) with polystyrene (PS) as a calibration standard. More specifically, 200 mg of polysaccharide is diluted in 200 ml of dimethylformamide (DMF) solvent to prepare a sample of approximately 1000 ppm, and the weight-average molecular weight can be measured using an Agilent 1200 series GPC instrument with an RI detector at a flow rate of 1 ml / min. In this case, the molecular weight of the sample can be calculated based on a calibration curve prepared using eight PS standards.

[0040] The polysaccharide may be a starch containing amylose and amylopectin in a weight ratio of 1:99 to 50:50 based on the total weight, but it is advantageous for the amylopectin content to be equal to or greater than the amylose content in terms of processability and solubility. Such modified starch may be one or more starches modified from potato starch, corn starch, rice starch, wheat starch, tapioca starch, and sweet potato starch, with potato starch being more preferred because of its high amylopectin content.

[0041] The first crosslinking agent may also be a cyclic carboxylic acid anhydride. The term "first crosslinking agent" used herein is used to distinguish it from the second crosslinking agent typically used to crosslink the surface of superabsorbent resin particles, and serves to link the hydroxyl groups of multiple polysaccharides together. The crosslinking in this step is performed without distinguishing between the surface and the interior. However, when an additional crosslinking step of superabsorbent resin particles is performed, the surface of the superabsorbent resin particles produced as a result of the crosslinking is primarily formed by the second crosslinking agent, while the interior is primarily formed by the first crosslinking agent. Therefore, the second crosslinking agent primarily functions to crosslink the surface of the superabsorbent resin, and therefore serves as a surface crosslinking agent. The first crosslinking agent, distinct from the second crosslinking agent, serves as an internal crosslinking agent.

[0042] Here, the cyclic carboxylic acid anhydride refers to a compound having a -(C=O)-O-(C=O)- linkage structure in a ring structure, and is prepared by removing a water molecule through a condensation reaction of two carboxylic acids.

[0043] Specifically, the cyclic carboxylic acid anhydride may be represented by the following chemical formula 1-1 or 1-2.

[0044] [ka]

[0045] In the above chemical formulas 1-1 and 1-2, n is 0 or 1, A is a cyclohexane; cyclohexene; cyclohexadiene; or benzene ring fused to adjacent five-membered rings; R is halogen, C 1-4 Alkyl, OH, or -(C 1-4 alkylene)-COOH, a is an integer from 0 to 4, b is an integer from 0 to 6; When a and b are each 2 or more, the two or more Rs are the same or different.

[0046] For example, R can be fluoro, chloro, bromo, methyl, OH, or -(methylene)-COOH.

[0047] In addition, a may be 0, 1, or 2, and b may be 0, 1, 2, 3, or 4.

[0048] For example, the cyclic carboxylic acid anhydride may be any one selected from the group consisting of the following, but is not limited thereto:

[0049] [ka]

[0050] Among these, succinic anhydride or citric acid is preferably used as the first crosslinking agent in terms of ease of use, ease of reaction, and formation of a crosslinked polymer network suitable for retaining water.

[0051] On the other hand, when a crosslinking agent that is not a cyclic carboxylic acid anhydride but is used as the first crosslinking agent is one that is used in general superabsorbent resins, such as N,N'-methylenebisacrylamide (MBA), ethylene glycol di(meth)acrylate, ethylene glycol diglycidyl ether, or epichlorohydrin, the crosslinking reaction may not occur, and the superabsorbent resin may not function as it should.

[0052] Furthermore, when divinyl sulfone is used as the first crosslinking agent, the water retention capacity and pressure absorption capacity of the final superabsorbent resin may both be reduced compared to when a cyclic carboxylic acid anhydride is used as the first crosslinking agent. This is because divinyl sulfone forms crosslinks by addition polymerization rather than condensation reaction, but the unmodified or acidic group-containing modified polysaccharide has a significantly low possibility of undergoing addition polymerization reaction, and therefore crosslinking by divinyl sulfone does not occur sufficiently.

[0053] Therefore, considering that the water retention capacity and pressure absorption capacity, which are the physical properties of superabsorbent resins, are in a trade-off relationship, it can be seen that superabsorbent resins containing a base resin containing a crosslinked polymer of polysaccharide and cyclic carboxylic acid anhydride exhibit significantly improved physical properties compared to superabsorbent resins containing a base resin containing a crosslinked polymer with other crosslinking agents.

[0054] The first crosslinking agent may be contained in the crosslinked polymer in an amount of 0.01 to 50 moles per mole of the polysaccharide. If the content of the first crosslinking agent is too low, crosslinking may be insufficient, making it difficult to achieve an appropriate level of strength. If the content of the first crosslinking agent is too high, the internal crosslink density may be high, making it difficult to achieve the desired water retention capacity. Specifically, the first crosslinking agent may be contained in the crosslinked polymer in an amount of 0.05 moles or more, 0.1 moles or more, 0.5 moles or more, 1 mole or more, 5 moles or more, 10 moles or more, 15 moles or more, or 18 moles or more, and 40 moles or less, 30 moles or less, 25 moles or less, or 20 moles or less, per mole of the polysaccharide.

[0055] More specifically, the content of the first crosslinking agent may vary depending on whether the polysaccharide is modified or not.

[0056] For example, when the superabsorbent resin contains a crosslinked polymer of a non-modified polysaccharide, the crosslinked polymer contains a carboxyl group (COOH) or a carboxylate group (COO) that can ensure the absorption performance of the superabsorbent resin. - For the introduction of the first crosslinking agent, the crosslinked polymer may contain 5 to 30 moles of the first crosslinking agent per mole of the polysaccharide. Specifically, when the superabsorbent resin contains a crosslinked polymer of a non-modified polysaccharide, the crosslinked polymer may contain 5 moles or more, 10 moles or more, 15 moles or more, or 18 moles or more of the first crosslinking agent per mole of the polysaccharide, and 30 moles or less, 25 moles or less, or 20 moles or less of the first crosslinking agent.

[0057] In contrast, when the superabsorbent resin contains a crosslinked polymer of a modified polysaccharide containing an acidic group such as a carboxyl group, the first crosslinker may be contained in the crosslinked polymer in an amount of 0.01 to 3 moles per mole of the polysaccharide. Specifically, when the superabsorbent resin contains a crosslinked polymer of a modified polysaccharide containing an acidic group, the first crosslinker may be contained in the crosslinked polymer in an amount of 0.01 moles or more, 0.05 moles or more, 0.1 moles or more, or 0.5 moles or more, and 3 moles or less, 2 moles or less, 1.5 moles or less, or 1 mole or less, per mole of the polysaccharide.

[0058] In addition, the first crosslinking agent may not contain an acrylate-based compound such as polyethylene glycol (meth)acrylate, polyethylene glycol di(meth)acrylate, or propylene glycol di(meth)acrylate; an epoxy-based compound such as diepoxybutane, diglycidyl ether, or ethylene glycol diglycidyl ether; divinyl sulfone; or epichlorohydrin, which are typically used in crosslinking polymerization of ethylenically unsaturated monomers.

[0059] Therefore, the crosslinked polymer has a structure in which polysaccharides are crosslinked by a first crosslinking agent containing a cyclic carboxylic acid anhydride, and has a three-dimensional network structure in which main chains of multiple polysaccharides are crosslinked by a ring-opening reaction of the cyclic carboxylic acid anhydride, which is the first crosslinking agent. When the crosslinked polymer has this three-dimensional network structure, the water retention capacity and pressure absorption capacity, which are various physical properties of the superabsorbent polymer, can be significantly improved compared to when the crosslinked polymer has a two-dimensional linear structure that is not additionally crosslinked by the first crosslinking agent.

[0060] More specifically, the polysaccharide includes a glycose repeating unit represented by the following chemical formula A. In this case, the first crosslinker may be bonded to the hydroxy group at the carbon at position 2 (C2), the carbon at position 3 (C3), or the carbon at position 6 (C6) in the repeating unit. The first crosslinker is primarily bonded to the carbon at position 6 (C6) because the hydroxy group at position 6 has higher reactivity than the hydroxy groups at positions 2 and 3. When the polysaccharide includes a glucosamine / N-acetylglucosamine repeating unit, the first crosslinker may also be primarily bonded to the hydroxy group at position 6 (C6).

[0061] [ka]

[0062] For example, when succinic anhydride is used as the first crosslinker, the crosslinked polymer may have a crosslinked structure represented by the following chemical formula B:

[0063] [ka]

[0064] In this case, the crosslinked polymer may be produced using only the polysaccharide as a monomer, without using an acrylic acid-based monomer, which is typically used in the production of superabsorbent polymers. This is because, when the crosslinked polymer is a crosslinked polymer of a polysaccharide, an acrylic acid-based monomer, and a first crosslinking agent, the crosslinked structure formed by the acrylic acid-based monomer may significantly reduce the biodegradability of the superabsorbent polymer.

[0065] Furthermore, the biodegradable superabsorbent resin has a structure in which at least a portion of the base resin is crosslinked by the second crosslinking agent. Specifically, the structure in which at least a portion of the base resin is crosslinked by the second crosslinking agent refers to a crosslinked layer formed on the base resin, containing a crosslinked polymer in which the crosslinked polymer is further crosslinked via the second crosslinking agent. Here, the crosslinked layer is formed mainly on at least a portion of the surface of each particle of the base resin, and has a structure in which the crosslinked polymer in the base resin is crosslinked by the second crosslinking agent. This is intended to increase the crosslink density on the surface of the superabsorbent resin. Therefore, when the superabsorbent resin further includes a structure in which at least a portion of the base resin is crosslinked by the second crosslinking agent, the structure has a higher crosslink density on the outside than on the inside.

[0066] In this case, an epoxy-based compound is used as the second crosslinking agent. This method has the advantage of being able to crosslink at a lower temperature than when commonly used alcohol-based compounds such as 1,4-butanediol, 1,3-butanediol, 1,5-pentanediol, 1,6-hexanediol, or 1,2-cyclohexanedimethanol are used as the second crosslinking agent. Specifically, polysaccharide compounds may be denatured at the crosslinking reaction temperature using alcohol-based compounds. Therefore, since a low temperature is required for the crosslinking reaction, the epoxy-based compound is considered to be suitable for the crosslinking reaction of a base resin containing a crosslinked polymer of polysaccharide.

[0067] More specifically, the epoxy compound may be a polyepoxy compound or an epihalohydrin compound.

[0068] For example, the polyfunctional epoxy compound is a compound containing two or more epoxy groups in the molecule, and may be one or more selected from the group consisting of ethylene glycol diglycidyl ether, diethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, tripropylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, neopentyl glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, polytetramethylene glycol diglycidyl ether, glycerol diglycidyl ether, glycerol triglycidyl ether, diglycerol polyglycidyl ether, polyglycerol polyglycidyl ether, resorcinol diglycidyl ether, 2,2-dibromoneopentyl glycol diglycidyl ether, trimethylolpropane triglycidyl ether, pentaerythritol polyglycidyl ether, sorbitol polyglycidyl ether, adipic acid diglycidyl ester, and phthalic acid diglycidyl ester.

[0069] The epihalohydrin compound may be at least one selected from the group consisting of epichlorohydrin, epiiodohydrin, epibromohydrin, and 2-(chloromethyl)-2-methyloxirane.

[0070] The superabsorbent polymer may also be in the form of particles having an average particle size of 150 to 850 μm. This particle size may be measured according to the EDANA WSP 220.3 method of the European Disposables and Nonwovens Association (EDANA). More specifically, the superabsorbent polymer composition may contain superabsorbent polymer particles with a particle size of about 150 to 850 μm, with about 90% by weight, preferably 95% by weight or more, based on the total weight, comprising superabsorbent polymer particles, and less than about 10% by weight, more specifically less than about 5% by weight, comprising fine powder with a particle size of less than about 150 μm. If the superabsorbent polymer contains a large amount of fine powder with a particle size of less than 150 μm, this is undesirable because it can degrade various physical properties of the superabsorbent polymer.

[0071] Furthermore, the biodegradable highly water-absorbent resin has an excellent balance between water retention capacity and absorbency under pressure.

[0072] Specifically, the biodegradable superabsorbent polymer may have a water retention capacity (CRC) of 10 to 50 g / g as measured by EDANA method WSP 241.3. For example, the biodegradable superabsorbent polymer may have a water retention capacity (CRC) of 11 g / g or more, 12 g / g or more, 20 g / g or more, 21 g / g or more, or 24 g / g or more, and 40 g / g or less, 35 g / g or less, 30 g / g or less, 25.5 g / g or less, or 25 g / g or less.

[0073] The biodegradable superabsorbent polymer may have an absorbent capacity under pressure (AUP) of 5 to 30 g / g at 0.7 psi as measured by EDANA method WSP 242.3. For example, the biodegradable superabsorbent polymer may have an absorbent capacity under pressure (AUP) of 7 g / g or more, 8 g / g or more, 9 g / g or more, 10 g / g or more, 11 g / g or more, 12 g / g or more, 13 g / g or more, 14 g / g or more, or 15 g / g or more, and 25 g / g or less, 23 g / g or less, 20 g / g or less, or 17 g / g or less.

[0074] Therefore, the biodegradable highly absorbent polymer may have an effective absorbent capacity (EFFC) calculated by the following Equation 1 of 10 g / g or more, or 10 g / g to 20 g / g.

[0075] [Formula 1] Effective Absorbent Capacity (EFFC) = {Water Retention Capacity (CRC) + Absorbent Capacity under 0.7 psi Pressure (AUP)} / 2

[0076] In the formula 1, The water retention capacity (CRC) means the centrifuge retention capacity (CRC) of the superabsorbent polymer measured by the EDANA method WSP 241.3; The absorbent capacity under 0.7 psi pressure (AUP) means the absorbent capacity under 0.7 psi pressure (AUP) of the superabsorbent polymer measured by the EDANA method WSP 242.3.

[0077] For example, the biodegradable superabsorbent polymer may have an effective absorbent capacity (EFFC) calculated by Equation 1 of 10 g / g or more, 15 g / g or more, 16 g / g or more, 17 g / g or more, or 18 g / g or more, and 20 g / g or less, or 19.5 g / g or less.

[0078] Furthermore, the biodegradable highly water-absorbent resin may have a degree of biodegradation measured according to ISO 14855-12005 of more than 30%, 40% or more, 50% or more, 60% or more, 70% or more, 80% or more, or 90% or more, but not more than 100%.

[0079] Manufacturing method of biodegradable superabsorbent resin Meanwhile, the biodegradable highly water-absorbent resin may be produced by the following production method.

[0080] Step 1: crosslinking an unmodified or acid group-containing modified polysaccharide in the presence of a first crosslinking agent to produce a crosslinked polymer; Step 2: Drying and grinding the crosslinked polymer to produce a base resin; and (Step 3) crosslinking at least a portion of the base resin in the presence of a second crosslinker, The first crosslinking agent includes a cyclic carboxylic acid anhydride, the second crosslinking agent includes an epoxy compound, and the explanations of the other terms refer to those described above.

[0081] Hereinafter, each step of the method for preparing a superabsorbent resin according to an embodiment will be described in more detail.

[0082] (Step 1) In one embodiment of the method, step 1 is a step of cross-linking a polysaccharide in the presence of a first cross-linking agent to produce a cross-linked polymer. To this end, a first cross-linking solution containing the first cross-linking agent and the polysaccharide is prepared.

[0083] The cross-linking polymerization is carried out by an esterification reaction between the polysaccharide and the first cross-linking agent. Specifically, after the cyclic carboxylic acid anhydride is ring-opened by a reaction catalyst (described later), the hydroxyl group at carbon C6 at the 6th position of the glycose repeating unit in the polysaccharide reacts with the carboxylic acid group of the cyclic carboxylic acid anhydride to form an ester group, thereby cross-linking the polysaccharide with the first cross-linking agent.

[0084] In this case, the first crosslinking agent may be used in an amount of 0.01 to 50 moles per mole of the polysaccharide. If the amount of the first crosslinking agent used is too low, crosslinking may not occur sufficiently, making it difficult to achieve an appropriate level of strength. If the amount of the first crosslinking agent used is too high, the internal crosslink density may increase, making it difficult to achieve the desired water retention capacity. Specifically, the first crosslinking agent may be used in an amount of 0.05 moles or more, 0.1 moles or more, 1 mole or more, 5 moles or more, 10 moles or more, 15 moles or more, or 18 moles or more, and 40 moles or less, 30 moles or less, 25 moles or less, or 20 moles or less, per mole of the polysaccharide.

[0085] During the crosslinking polymerization, a catalyst and / or a heat stabilizer may be further used to promote the esterification reaction.

[0086] The esterification catalyst may be 4-dimethylaminopyridine (DMAP), magnesium acetate, tetra-n-butyl titanate (TBT), lead acetate, sodium acetate, potassium acetate, antimony trioxide, N-methylimidazole, or a combination thereof. The catalyst may be used in an amount of 0.1 to 5 moles per mole of the polysaccharide to shorten the reaction time and achieve the desired degree of crosslinking. Specifically, the reaction catalyst may be used in an amount of 0.1 moles or more, 0.5 moles or more, 1 mole or more, or 2 moles or more, and 4.5 moles or less, 4 moles or less, or 3.5 moles or less per mole of the polysaccharide.

[0087] The heat stabilizer may be an organic or inorganic phosphorus compound. The organic or inorganic phosphorus compound may be, for example, phosphoric acid, an organic ester of phosphoric acid, phosphorous acid, or an organic ester of phosphorous acid. More specifically, commercially available substances such as phosphoric acid, alkyl phosphate, or aryl phosphate may be used as the heat stabilizer.

[0088] Furthermore, the first crosslinking solution may further contain additives such as a thickener, a plasticizer, a storage stabilizer, and an antioxidant, if necessary.

[0089] The first crosslinking solution may be in the form of a suspension if the polysaccharide is insoluble in a high molecular weight, or in the form of a solution dissolved in a solvent such as water if the polysaccharide is water-soluble. The solids content and the concentrations of the polysaccharide, first crosslinking agent, catalyst, and optionally, thermal stabilizer in the first crosslinking solution may be appropriately adjusted taking into account reaction conditions, etc. For example, the solids content in the first crosslinking solution may be 10 to 80 wt %, 15 to 60 wt %, or 30 to 50 wt %.

[0090] When the first crosslinking solution has a solid content within the above range, it is possible to eliminate the need to remove polysaccharides that have not participated in the crosslinking reaction by utilizing the gel effect that occurs in the polymerization reaction of a highly concentrated aqueous solution, and it is also advantageous for controlling the grinding efficiency when grinding the polymer, as described below.

[0091] The solvent used in this case is not limited to any particular composition as long as it can dissolve the above-mentioned components, and for example, one or more solvents selected from the group consisting of 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 amyl ketone, cyclohexanone, cyclopentanone, diethylene glycol monomethyl ether, diethylene glycol ethyl ether, toluene, xylene, butyrolactone, carbitol, methyl cellosolve acetate, and N,N-dimethylacetamide can be used in combination.

[0092] Meanwhile, the cross-linking reaction of the polysaccharide, i.e., the esterification reaction between the polysaccharide and the first cross-linking agent, may be carried out at a temperature of 25°C to 100°C for 1 hour to 24 hours. More preferably, the cross-linking reaction of the polysaccharide may be carried out at a temperature of 25°C to 30°C for 4 hours to 12 hours.

[0093] Furthermore, the method may further include a step of precipitating the crosslinked product in a water-miscible solvent after the crosslinking reaction of the polysaccharide. This precipitation process provides porosity to the superabsorbent resin particles, thereby improving the absorption capacity of the superabsorbent resin.

[0094] In this case, before the precipitation process, a step of mixing the crosslinked product produced by the crosslinking reaction of the polysaccharide with a basic solution to neutralize it to a pH of 6 to 8 may be further carried out. This neutralizes the carboxyl groups present in the crosslinked product to carboxylate groups, thereby further improving the absorption performance of the crosslinked product and allowing the crosslinked product to exhibit neutrality suitable for use in sanitary products.

[0095] Here, a water-miscible solvent means that after mixing water and the solvent, after a certain period of time, for example, about 5 minutes, 50% or more, or 80 to 100% of the two fluid layers do not separate into separate layers and remain as a single layer. For example, water-miscible solvents may include, but are not limited to, lower monohydric alcohols such as methanol, ethanol, propanol, and isopropanol; acetone; and 1,4-dioxane.

[0096] The resulting crosslinked polymer may be several centimeters to several millimeters in size. Specifically, the size of the resulting crosslinked polymer varies depending on the concentration of the first crosslinking agent injected and the injection rate, but typically, a crosslinked polymer with a weight average particle size of 2 to 50 mm is obtained.

[0097] (Step 2) Next, the cross-linked polymer is dried and ground to produce a base resin.

[0098] Meanwhile, after preparing the crosslinked polymer, a coarse pulverization process for pulverizing the prepared crosslinked polymer may be optionally performed before the subsequent drying and pulverization processes.

[0099] The coarse pulverization process is a process for increasing the drying efficiency in the subsequent drying process and controlling the particle size of the superabsorbent resin powder to be finally produced. The pulverizer used here is not limited in terms of its configuration, and specifically may include any one selected from the group of pulverizing devices consisting of a vertical pulverizer, a turbo cutter, a turbo grinder, a rotary cutter mill, a cutter mill, a disc mill, a shred crusher, a crusher, a meat chopper, and a disc cutter, but is not limited to the above examples.

[0100] For example, the coarse pulverization process may be performed until the particle size of the crosslinked polymer reaches about 2 to about 10 mm. Pulverizing the crosslinked polymer to a particle size of less than 2 mm is technically difficult due to the high moisture content of the crosslinked polymer, and the pulverized particles may aggregate together. Meanwhile, pulverizing the crosslinked polymer to a particle size of more than 10 mm results in little increase in the efficiency of the subsequent drying step.

[0101] The coarsely ground crosslinked polymer is then dried, ground, and optionally classified to produce the base resin.

[0102] The drying method may be selected from any method commonly used in the drying process of crosslinked polymers without being limited to the specific structure. Specifically, the drying step may be carried out by a method such as hot air supply, infrared radiation, ultrashort wave radiation, or ultraviolet radiation.

[0103] Specifically, the drying may be performed under vacuum conditions at a temperature of 100° C. to about 180° C. Meanwhile, the drying time may be, but is not limited to, about 20 to about 90 minutes, taking into consideration process efficiency.

[0104] After such a drying step, the polymer may have a moisture content of about 5 to about 10% by weight.

[0105] After the drying step, a pulverization step is carried out.

[0106] The pulverization process may be carried out so that the particle size of the polymer powder, i.e., the base resin, is about 150 to about 850 μm. Specific examples of the pulverizer used to pulverize to such a particle size include a pin mill, hammer mill, screw mill, roll mill, disc mill, and jog mill, but the present invention is not limited to these examples.

[0107] After the pulverization step, the pulverized polymer powder may be further classified according to particle size in order to control the physical properties of the superabsorbent resin to be manufactured as a final product.

[0108] The base resin obtained as a result of the above process may be in the form of a powder containing a crosslinked polymer crosslinked by the acrylic acid-based monomer and the first crosslinking agent. Specifically, the base resin may be in the form of a powder having a particle size of 150 to 850 μm.

[0109] (Step 3) Next, a step of crosslinking at least a portion of the base resin in the presence of a second crosslinking agent is performed. In this step, the crosslinked polymer contained in the base resin may be additionally crosslinked via the second crosslinking agent to form a crosslinked layer. In other words, it is possible to obtain superabsorbent resin particles having a crosslinked layer formed on at least a portion of the surface of the base resin particles.

[0110] The second crosslinking agent used here is the same as that described above and may be used in an amount of 0.01 to 5 parts by weight per 100 parts by weight of the base resin. If the content of the second crosslinking agent relative to the base resin is too low, the surface modification may not be properly performed, and the pressure absorption capacity of the final superabsorbent resin may decrease. Conversely, if an excessive amount of the second crosslinking agent is used, excessive crosslinking reaction may actually decrease the basic water retention capacity of the resin, which is undesirable. More specifically, the second crosslinking agent may be used in an amount of 0.02 parts by weight or more, 0.05 parts by weight or more, 0.1 parts by weight or more, and 4 parts by weight or less, 3 parts by weight or less, 2 parts by weight or less, 1 part by weight or less, or 0.5 parts by weight or less per 100 parts by weight of the base resin.

[0111] The method for mixing the second crosslinking agent with the base resin is not limited to a specific configuration, and may include mixing the second crosslinking agent and base resin powder in a reaction vessel, spraying the second crosslinking agent onto the base resin powder, or continuously feeding the base resin and the second crosslinking agent into a continuously operated mixer and mixing them.

[0112] More preferably, the second crosslinking agent may be added in the form of a second crosslinking solution mixed in a solvent containing water. When water is added, the second crosslinking agent is advantageously dispersed evenly in the polymer.

[0113] The added water induces uniform dispersion of the second crosslinking agent, prevents aggregation of the polymer powder, and optimizes the surface penetration depth of the second crosslinking agent. The amount of water is preferably 1 to 20 parts by weight per 100 parts by weight of the base resin. For example, the amount of water may be 1 part by weight or more, 2 parts by weight or more, 3 parts by weight or more, or 4 parts by weight or more, and 10 parts by weight or less, 9 parts by weight or less, 8 parts by weight or less, 7 parts by weight or less, 6 parts by weight or less, or 5 parts by weight or less, per 100 parts by weight of the base resin.

[0114] The second cross-linking solution may further contain methanol. In particular, the second cross-linking solution may contain water and methanol in a weight ratio of 60:40 to 40:60. Preferably, the second cross-linking solution may contain water and methanol in a weight ratio of 50:50.

[0115] Additionally, the crosslinking in step 3 may be performed by heating the base resin powder to which the second crosslinking solution has been added at a temperature of 80 to 140° C. More specifically, the crosslinking in step 3 may be performed by increasing the temperature from an initial temperature of 20 to 80° C. to a maximum temperature of 80 to 140° C. over a period of 10 to 30 minutes, and maintaining the maximum temperature for 5 to 60 minutes.

[0116] By satisfying the conditions for the crosslinking process in step 3, a superabsorbent resin having the proper physical properties of an embodiment can be more effectively produced.

[0117] The heating means for crosslinking in step 3 is not particularly limited. Heating may be performed by supplying a heat medium or by directly supplying a heat source. Usable types of heat medium include, but are not limited to, heated fluids such as steam, hot air, and hot oil. The temperature of the supplied heat medium may be appropriately selected taking into consideration the heat medium, the rate of temperature rise, and the target temperature. Directly supplied heat sources include, but are not limited to, electrical heating and gas heating.

[0118] The superabsorbent polymer obtained by the above-described manufacturing method maintains excellent absorption performance such as water retention capacity and pressure absorption capacity, and can satisfy various physical properties of one embodiment, such as improved absorption speed.

[0119] Also provided is an article comprising the aforementioned biodegradable superabsorbent polymer.

[0120] The article may be one or more selected from water-absorbent articles, sanitary products, soil water retention agents, civil engineering water-stopping materials, construction water-stopping materials, seedling sheets, freshness-preserving agents, compress materials, electrical insulators, oral care articles, dental care articles, cosmetic articles, and skin care articles.

[0121] Examples of sanitary products containing the superabsorbent polymer include baby diapers, adult diapers, and sanitary napkins. The superabsorbent polymer is particularly suitable for adult diapers, where secondary odors caused by bacterial growth are a particular problem. These sanitary products may have the same structure as conventional sanitary products, except that the absorbent core contains the superabsorbent polymer of the embodiment described above.

[0122] Preferred examples are presented below to aid in understanding the invention, but the following examples are merely for illustrative purposes and are not intended to limit the invention.

[0123] <Example> Example 1 (Step 1) 100 g of starch (soluble starch, Sigma-Aldrich) was dissolved in 5 L of water and stirred for 10 minutes while heating to 90°C. After cooling to room temperature, 240 g of 4-dimethylaminopyridine (DMAP) (1.05 equivalents relative to the hydroxyl groups of the starch, 3.15 moles per mole of starch) was added and dissolved in the reactor as a catalyst. 1000 g of succinic anhydride (6 equivalents relative to the hydroxyl groups of the starch monomer, 18 moles per mole of starch monomer) was then added to obtain a first crosslinking solution. This solution was stirred at room temperature (approximately 25°C) for 6 hours to carry out the crosslinking reaction. The solution was then neutralized to pH 7 with 10% sodium hydroxide solution and precipitated in 5 L of methanol to obtain a crosslinked polymer.

[0124] (Step 2) The cross-linked polymer was then cut into pieces approximately 5 cm x 5 cm in size and placed in a meat chopper to crush the polymer, yielding gel particle crumbs with sizes ranging from 1 mm to 10 mm. The crumbs were then dried in an oven capable of vertical airflow. Hot air at 120°C or higher was blown from bottom to top for 15 minutes, then from top to bottom for another 15 minutes, ensuring uniform drying, until the moisture content of the dried product was 2% or less. After drying, the crumbs were crushed in a crusher and classified to select particles ranging from 150 to 850 μm in size, preparing the base resin.

[0125] (Step 3) A second crosslinking solution containing 0.1 parts by weight of a second crosslinking agent, ethylene glycol diglycidyl ether (Denacol® EX-810, Nagase Chemtex), 4 parts by weight of water, and 4 parts by weight of methanol, based on 100 parts by weight of base resin, was sprayed onto the prepared base resin powder and stirred at room temperature to evenly distribute the second crosslinking solution over the base resin powder. Next, the base resin powder mixed with the second crosslinking solution was placed in a crosslinking reactor to carry out the crosslinking reaction.

[0126] In this crosslinking reactor, the base resin powder was gradually heated from an initial temperature of around 80°C, and after 30 minutes, the maximum reaction temperature of 100°C was reached. After reaching this maximum reaction temperature, the reaction was continued for an additional 15 minutes, and then a sample of the final superabsorbent resin was taken. The sample was then classified using a standard ASTM mesh sieve to produce the superabsorbent resin of Example 1 having a particle size of 150 μm to 850 μm.

[0127] Example 2 A superabsorbent polymer was prepared in the same manner as in Example 1, except that chitosan (medium molecular weight, 200-800 cP, 1 wt.% in 1% acetic acid (25°C, Brookfield), Sigma-Aldrich) was used instead of starch as the monomer.

[0128] Example 3 (Step 1-1) 100 g of starch (soluble starch, manufactured by Sigma-Aldrich) was dispersed in 300 g of ethanol, and then 70 mL of 11.5 M NaOH aqueous solution was added and stirred for 20 minutes. 37.5 g of sodium chloroacetate was then added, and the mixture was stirred for 3 hours while heating to 70°C. After stirring was completed, the solvent was removed and the mixture was neutralized with 1 M HCl solution. After washing three times with a 4:1 (weight ratio) ethanol / water solution, ethanol precipitation was performed to synthesize a modified starch precursor containing acidic groups. The synthesized modified starch precursor containing acidic groups was carboxymethylated starch, and the degree of substitution of the carboxymethyl groups was 0.71. The degree of substitution of the carboxymethyl groups of the carboxymethylated starch was 1 The integral sum of the peaks in the data analysis range of 4 to 5.5 ppm in the H NMR spectrum was set to 1, and the degrees of substitution at the 2nd, 3rd, and 6th carbons were calculated, and then these were added together. 1 H NMR was performed by adding carboxymethylated starch dissolved in H2O to MeOH, stirring, filtering, and then drying the prepared sample. The sample was dissolved in 0.75 mL of D2O and 0.25 mL of D2SO4, which are NMR measurement solvents, and stirred at 90 °C for 1 hour.

[0129] (Step 1-2) 90 g of the precursor prepared in step 1-1 was dissolved in 150 g of water, and then 9 g of citric anhydride (2-(3-hydroxy-2,5-dioxotetrahydrofuran-3-yl)acetic acid) (0.1 mole per mole of the modified starch precursor containing acidic groups) was added to obtain a first crosslinking solution. This was stirred at 60°C for 2 hours to carry out a crosslinking reaction, and then heat-cured and dried in an oven at 120°C until all the solvent was removed, obtaining a crosslinked polymer.

[0130] Thereafter, steps 2 and 3 were carried out in the same manner as in Example 1 to produce the superabsorbent resin of Example 3.

[0131] Example 4 A superabsorbent resin was prepared in the same manner as in Example 1, except that the second crosslinking agent, ethylene glycol diglycidyl ether, was used in an amount of 0.02 parts by weight based on 100 parts by weight of the base resin.

[0132] Example 5 A superabsorbent resin was prepared in the same manner as in Example 1, except that the second crosslinking agent, ethylene glycol diglycidyl ether, was used in an amount of 0.5 parts by weight based on 100 parts by weight of the base resin.

[0133] Example 6 A superabsorbent polymer was prepared in the same manner as in Example 3, except that succinic anhydride was used as the first crosslinking agent in place of citric anhydride in an amount of 3 moles per mole of monomer-modified starch.

[0134] Example 7 A superabsorbent polymer was prepared in the same manner as in Example 3, except that succinic anhydride was used as the first crosslinking agent in an amount of 1 mole per mole of the monomer-modified starch instead of citric anhydride.

[0135] Example 8 A superabsorbent resin was prepared in the same manner as in Example 3, except that succinic anhydride was used as the first crosslinking agent instead of citric anhydride.

[0136] Example 9 A superabsorbent resin was prepared in the same manner as in Example 3, except that citric anhydride, the first crosslinking agent, was used in an amount of 0.5 mol per 1 mol of the monomer-modified starch.

[0137] Example 10 A superabsorbent resin was prepared in the same manner as in Example 3, except that the first crosslinking agent, citric anhydride, was used in an amount of 0.05 mol per 1 mol of the monomer-modified starch.

[0138] Example 11 A superabsorbent resin was prepared in the same manner as in Example 1, except that the second crosslinking agent, ethylene glycol diglycidyl ether, was used in an amount of 0.05 parts by weight based on 100 parts by weight of the base resin.

[0139] Example 12 A superabsorbent resin was prepared in the same manner as in Example 1, except that epichlorohydrin was used in an amount of 0.05 parts by weight per 100 parts by weight of the base resin instead of ethylene glycol diglycidyl ether as the second crosslinking agent.

[0140] Example 13 A superabsorbent resin was prepared in the same manner as in Example 3, except that the second crosslinking agent, ethylene glycol diglycidyl ether, was used in an amount of 0.05 parts by weight based on 100 parts by weight of the base resin.

[0141] Example 14 A superabsorbent resin was prepared in the same manner as in Example 3, except that epichlorohydrin was used in an amount of 0.05 parts by weight per 100 parts by weight of the base resin instead of ethylene glycol diglycidyl ether as the second crosslinking agent.

[0142] Comparative Example 1 (Step 1) 100 g of starch (soluble starch, manufactured by Sigma-Aldrich) was added to a reactor as a monomer and 300 mL of water. The mixture was heated to 90°C and stirred for 1 hour, then cooled to room temperature. Next, a solution of 150 g of acrylic acid neutralized to 95% with 40% NaOH was added to the reactor. Next, 3.2 g of ammonium persulfate (APS) as a polymerization initiator and 0.24 g of N,N'-methylenebisacrylamide (MBA) as a first crosslinking agent were added to the reactor to obtain a first crosslinking solution. The mixture was heated to 65°C and stirred for 4 hours to carry out the crosslinking reaction, resulting in a crosslinked polymer.

[0143] Thereafter, steps 2 and 3 were carried out in the same manner as in Example 1 to produce a superabsorbent resin of Comparative Example 1.

[0144] Comparative Example 2 A superabsorbent resin was prepared in the same manner as in Example 3, except that divinyl sulfone was used as the first crosslinking agent in place of citric anhydride in an amount of 0.05 mol per 1 mol of the monomer-modified starch.

[0145] Experimental example: Measurement of the physical properties of superabsorbent resin The physical properties of the superabsorbent polymers prepared in the examples and comparative examples were evaluated by the following methods and are shown in Table 1 below. Unless otherwise specified, all of the following physical property evaluations were carried out in a constant temperature and humidity chamber (23±0.5°C, relative humidity 45±0.5%), and the average of three measurements was used to prevent measurement errors. Furthermore, the physiological saline or salt water used in the following physical property evaluations refers to a 0.9 wt% sodium chloride (NaCl) aqueous solution.

[0146] (1)Centrifuge Retention Capacity (CRC) The water retention capacity of each resin was measured by the absorbency under no load using EDANA WSP 241.3.

[0147] Specifically, a superabsorbent resin W0 (g) (approximately 0.2 g) was evenly placed in a nonwoven fabric envelope, sealed, and then immersed in physiological saline (0.9 wt%) at room temperature. After 30 minutes, the envelope was centrifuged at 250 G for 3 minutes to remove water, and the mass of the envelope W2 (g) was measured. The same procedure was repeated without the resin, and the mass W1 (g) was then measured. The CRC (g / g) was calculated using the obtained masses according to the following formula:

[0148] [Formula 1] CRC(g / g)={[W2(g)-W1(g)] / W0(g)}-1

[0149] (2) Absorbency Under Pressure (AUP) The 0.7 psi pressure absorbency of each resin was measured by EDANA method WSP 242.3.

[0150] Specifically, a 400-mesh stainless steel iron net was attached to the bottom of a plastic cylinder with an inner diameter of 60 mm. Under conditions of room temperature and 50% humidity, superabsorbent resin W0 (g) (0.90 g) was evenly spread on the iron net, and a piston capable of applying a uniform load of 0.3 psi was placed on top of it. The piston was slightly smaller than the outer diameter of 60 mm, with no gap between it and the inner wall of the cylinder so as not to hinder its up and down movement. At this point, the weight of the device, W3 (g), was measured.

[0151] A glass filter with a diameter of 90 mm and a thickness of 5 mm was placed inside a Petri dish with a diameter of 150 mm, and physiological saline solution composed of 0.9 wt% sodium chloride was placed at the same level as the top surface of the glass filter. A sheet of filter paper with a diameter of 90 mm was placed on top of the filter. The measuring device was placed on the filter paper and allowed to absorb the liquid under load for 1 hour. After 1 hour, the measuring device was lifted and its weight W4 (g) was measured.

[0152] Using the obtained masses, the absorbency under pressure (g / g) was calculated according to the following formula.

[0153] [Formula 2] AUP(g / g) = [W4(g) - W3(g)] / W0(g)

[0154] (3) Effective Absorption Capacity (EFFC) Based on the centrifuge retention capacity (CRC) and absorbent capacity under 0.7 psi pressure (AUP) measured above, the effective absorbent capacity (EFFC) was calculated according to Equation 1 above.

[0155] (4) Biodegradability The biodegradability of the superabsorbent polymers produced in the Examples and Comparative Examples was measured using a biodegradability tester (ECHO INSTRUMENTS' 12-Channel Respirometer) in accordance with ISO 14855-12005, a standard for measuring the respiratory biodegradability of plastic materials under composting conditions, by quantifying and calculating the amount of carbon dioxide released by the metabolism of microorganisms in each superabsorbent polymer. Specifically, each superabsorbent polymer test material was composted under composting conditions for six months, and the biodegradability was calculated as the ratio of the theoretical amount of carbon dioxide released from the test material to the actual amount of carbon dioxide released from the test material.

[0156] Here, the theoretical carbon dioxide generation amount and biodegradability are calculated by the following Equations 3 and 4, respectively.

[0157] [Formula 3] Theoretical carbon dioxide generation (ThCO2; g / container) = M TOT ×C TOT ×44 / 12

[0158] In the above formula 3, M TOT means the amount (g) of total dry solids of the test substance added to the compost at the start of the test, C TOT means the proportion of organic carbon contained in the total dry solids of the test material (g / g); 44 means the molecular weight of carbon dioxide, 12 means the atomic weight of carbon,

[0159] [Formula 4] Biodegradation (%)=[{(CO2) T -(CO2) B} / ThCO2]×100

[0160] In the above formula 4, (CO2) T is the cumulative amount of carbon dioxide generated from the composting container containing the test material (g / container), (CO2) B is the average cumulative amount of carbon dioxide generated from the inoculum container (g / container), ThCO2 is the theoretical carbon dioxide generation amount (g / container) calculated through Equation 3.

[0161] [Table 1]

[0162] As can be seen from Table 1, the superabsorbent resins of the examples, which contain a base resin containing a crosslinked polymer obtained by crosslinking an unmodified or acidic group-containing modified polysaccharide using a cyclic carboxylic acid anhydride as a first crosslinking agent, and in which at least a portion of the base resin is crosslinked using a second crosslinking agent, exhibit excellent biodegradability compared to the superabsorbent resins of the comparative examples, without any decrease in the physical properties of general superabsorbent resins, such as water retention capacity and pressure absorption capacity.

[0163] Specifically, it was confirmed that the superabsorbent resin of Example 1, which was produced using only polysaccharide as a monomer, had a significantly improved biodegradability value while exhibiting the same levels of pressurized water retention capacity and absorption capacity as the superabsorbent resin of Comparative Example 1, in which a crosslinked polymer was produced using both polysaccharide and acrylic acid as monomers.

[0164] Furthermore, the superabsorbent resin of Example 10, which contains a base resin containing a crosslinked polymer obtained by crosslinking an acidic group-containing modified polysaccharide monomer using a first crosslinking agent of a cyclic carboxylic acid anhydride, and in which at least a portion of the base resin is crosslinked using a second crosslinking agent of ethylene glycol diglycidyl ether, is found to exhibit significantly improved water retention capacity, pressure absorption capacity, and effective absorption capacity compared to the superabsorbent resin of Comparative Example 2, which was produced using the same monomer and second crosslinking agent and divinyl sulfone as the first crosslinking agent.

[0165] This indicates that when biodegradable superabsorbent polymers are produced using unmodified or acidic group-containing modified polysaccharides, the physical properties of the superabsorbent polymers vary depending on the type of first crosslinking agent. Furthermore, it can be seen that superabsorbent polymers having a three-dimensional network structure in which polysaccharides are crosslinked with ring-opened cyclic carboxylic acid anhydrides, and in which at least a portion of the surface of the crosslinked polymer is crosslinked with an epoxy compound, are suitable for biodegradable superabsorbent polymers.

Claims

1. A method for producing a polymer composition comprising: a base resin including a crosslinked polymer of a carboxymethylated polysaccharide and a first crosslinker; a biodegradable highly absorbent resin in which at least a portion of the base resin is crosslinked by a second crosslinking agent, the first crosslinking agent is a cyclic carboxylic acid anhydride, and is contained in the crosslinked polymer in an amount of 0.01 to 3 moles per mole of the polysaccharide; The second crosslinking agent is an epoxy compound and is used in an amount of 0.02 to 0.5 parts by weight based on 100 parts by weight of the base resin. Biodegradable super absorbent resin.

2. A method for producing a composition comprising: a base resin including a crosslinked polymer of an unmodified polysaccharide and a first crosslinker; a biodegradable highly absorbent resin in which at least a portion of the base resin is crosslinked by a second crosslinking agent, the first crosslinking agent is a cyclic carboxylic acid anhydride, and is contained in the crosslinked polymer in an amount of 15 to 30 moles per mole of the polysaccharide; The second crosslinking agent is an epoxy compound and is used in an amount of 0.02 to 0.5 parts by weight based on 100 parts by weight of the base resin. Biodegradable super absorbent resin.

3. The polysaccharide is at least one selected from the group consisting of starch, dextrin, and chitosan. The biodegradable highly absorbent resin according to claim 1 or 2.

4. The cyclic carboxylic acid anhydride is represented by the following chemical formula 1-1 or 1-2: The biodegradable highly absorbent resin according to claim 1 or 2. 【Chemical 1】 In the above chemical formulas 1-1 and 1-2, n is 0 or 1; A is a cyclohexane; cyclohexene; cyclohexadiene; or benzene ring fused to adjacent five-membered rings; R is halogen, C １－４ Alkyl, OH, or -(C １－４ alkylene)-COOH, a is an integer from 0 to 4; b is an integer from 0 to 6; When a and b are each 2 or more, the two or more Rs are the same or different.

5. The cyclic carboxylic acid anhydride is any one selected from the group consisting of: The biodegradable highly absorbent resin according to claim 1 or 2. 【Chemistry 2】

6. The epoxy compound is a polyepoxy compound or an epihalohydrin compound. The biodegradable highly absorbent resin according to claim 1 or 2.

7. The biodegradable superabsorbent polymer has an effective absorbent capacity (EFFC) of 10 g / g to 20 g / g, as calculated by the following formula 1: The biodegradable highly absorbent resin according to claim 1 or 2. [Formula 1] Effective Absorbent Capacity (EFFC) = {Water Retention Capacity (CRC) + Absorbent Capacity under 0.7 psi (AUP)} / 2 In the formula 1, The water retention capacity (CRC) means the centrifugation water retention capacity (CRC) of the superabsorbent polymer measured by the EDANA method WSP 241.3; The absorbent capacity under 0.7 psi pressure (AUP) means the absorbent capacity under 0.7 psi pressure (AUP) of the superabsorbent polymer measured by the EDANA method WSP 242.

3.

8. Step 1: crosslinking an unmodified or carboxymethylated polysaccharide in the presence of a first crosslinking agent to produce a crosslinked polymer; Step 2: drying and grinding the crosslinked polymer to produce a base resin; and (Step 3) crosslinking at least a portion of the base resin in the presence of a second crosslinker, the first cross-linking agent is a cyclic carboxylic acid anhydride, the second crosslinking agent is an epoxy compound; A method for producing the biodegradable highly water-absorbent resin according to claim 1 or 2.

9. The cross-linking of the polysaccharide is carried out at a temperature between 25° C. and 100° C. A method for producing the biodegradable highly water-absorbent resin according to claim 8.

10. Step 1 further comprises a step of precipitating the crosslinked product in a water-miscible solvent after the crosslinking reaction of the polysaccharide. A method for producing the biodegradable highly water-absorbent resin according to claim 8.

11. The second crosslinking agent is introduced in the form of a second crosslinking solution mixed in a solvent containing water. A method for producing the biodegradable highly water-absorbent resin according to claim 8.

12. The water is used in an amount of 1 to 20 parts by weight per 100 parts by weight of the base resin. A method for producing the biodegradable highly water-absorbent resin according to claim 11.

13. the second cross-linking solution further comprises methanol; A method for producing the biodegradable highly water-absorbent resin according to claim 11.

14. The water and methanol are present in a weight ratio of 60:40 to 40:

60. A method for producing the biodegradable highly water-absorbent resin according to claim 13.

15. The crosslinking in step 3 is carried out at a temperature of 80 to 140°C. A method for producing the biodegradable highly water-absorbent resin according to claim 8.

16. An article comprising the biodegradable highly absorbent polymer according to claim 1 or 2.

17. The article is at least one selected from the group consisting of water-absorbing articles, sanitary goods, soil water-retaining agents, civil engineering water-stopping materials, building water-stopping materials, seedling sheets, freshness-preserving agents, compress materials, electrical insulators, oral care articles, dental care articles, cosmetic articles, and skin care articles.

17. The article of claim 16.

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