Method for producing carboxyalkylated polysaccharides, and method for producing biodegradable superabsorbent resins using the same.

Abstract

The present invention relates to a method for producing a carboxyalkylated polysaccharide and a method for producing a biodegradable superabsorbent resin using the same. More specifically, the present invention relates to a method for producing a carboxyalkylated polysaccharide that exhibits high substitution efficiency by carrying out a carboxyalkylation reaction under high torque induced by gelatinization while using a specific content of water, and a method for producing a biodegradable superabsorbent resin that can produce a superabsorbent resin having high water retention capacity by self-crosslinking the carboxyalkylated polysaccharide produced by such a production method.

Description

[Technical Field]

[0001] [Cross-reference of related applications] This application claims priority based on Korean Patent Application No. 10-2022-0183169 dated December 23, 2022, and all content disclosed in the said Korean Patent Application is incorporated herein as part of this specification.

[0002] This invention relates to a method for producing carboxyalkylated polysaccharides, and a method for producing biodegradable superabsorbent resins using the same. [Background technology]

[0003] Recently, as interest in biomass materials has increased due to environmental concerns, there has been growing interest in biodegradable compounds such as polysaccharides, polyaspartic acid, and polyglutamic acid.

[0004] In particular, polysaccharides are widely present in nature as components of plants and animals, and are attracting attention as important biodegradable materials because they are economical and readily available. However, in order to be used in various industrial fields, it is necessary to replace the hydroxyl groups (-OH) present in polysaccharides with other functional groups, and methods for producing modified polysaccharides with various substituents have been investigated.

[0005] Among such modified polysaccharides, carboxyalkylated polysaccharides, in which carboxyl groups are introduced at the terminal groups, can be applied to various uses where the presence of acidic groups is required. In particular, carboxyalkylated polysaccharides can be used as the main raw material for biodegradable superabsorbent polymers. Superabsorbent polymers (SAPs) are synthetic polymers that have the function of absorbing water about 500 to 1000 times their weight, and are widely used not only in hygiene products such as children's diapers, but also in horticultural soil water retention agents, civil engineering and construction waterproofing materials, seedling sheets, freshness preservatives in the food distribution field, and materials for poultices and electrical insulation. Therefore, there is a need for research into methods of manufacturing carboxyalkylated polysaccharides in a way that allows for industrial mass production without causing environmental problems.

[0006] However, conventional carboxyalkylation reactions of polysaccharides have problems not only with their economic viability due to the alcoholic organic solvents used in the carboxyalkylation reaction, but also with the difficulty of mass production due to process issues. Furthermore, when large quantities of alcoholic organic solvents are used, expensive solvent recovery equipment is required to recover and reuse the solvent after the reaction.

[0007] Therefore, there is still a demand for an economical and large-scale production method for carboxyalkylated polysaccharides used in the manufacture of biodegradable superabsorbent polymers. As a result of diligent research into such methods, it was confirmed that this demand can be satisfied by using a specific amount of water as the sole solvent and carrying out the carboxyalkylation reaction of polysaccharides under high torque and temperature induced by gelatinization, thus completing the present invention. [Overview of the project] [Problems that the invention aims to solve]

[0008] The present invention relates to a method for producing carboxyalkylated polysaccharides and a method for producing a biodegradable superabsorbent resin using the same, more specifically, to a method for producing carboxyalkylated polysaccharides that exhibit high substitution efficiency by carrying out a carboxyalkylation reaction using a specific amount of water under high torque induced by gelatinization, and to a method for producing a biodegradable superabsorbent resin that can produce a superabsorbent resin with high water retention capacity by self-crosslinking the carboxyalkylated polysaccharide produced by such a method. [Means for solving the problem]

[0009] To solve the aforementioned problems, the present invention provides a method for producing carboxyalkylated polysaccharides, comprising the steps of mixing a polysaccharide, a hydroxide, a metal salt of a haloalkylcarboxylic acid, and water in a reactor to carry out gelatinization and carboxyalkylation reactions of the polysaccharide, wherein the water used is 0.35 to 1.0 times the weight of the polysaccharide, and the torque in the reactor is maintained at 7 to 18 Nm after the gelatinization of the polysaccharide.

[0010] Furthermore, the present invention provides a method for producing a biodegradable superabsorbent resin, comprising the following steps.

[0011] Step 1: Dissolve the carboxyalkylated polysaccharide produced by the above manufacturing method in 5 to 15 times the weight of the carboxyalkylated polysaccharide in water. Step 2 involves drying the product from Step 1 under pH 6 to 8 conditions while allowing it to self-crosslink. [Effects of the Invention]

[0012] The above-described method for producing a carboxyalkylated polysaccharide has the advantage that only a small amount of water is used as a solvent during the carboxyalkylation reaction, and the substitution efficiency of the carboxyalkyl group can be increased. Further, since the production method does not use an alcohol-based organic solvent as a reaction solvent, it is environmentally friendly and economical, and is suitable for mass-producing carboxyalkylated polysaccharides.

[0013] In addition, when the carboxyalkylated polysaccharide produced by the above production method is self-crosslinked, it is possible to produce a biodegradable superabsorbent resin having high water retention ability.

Brief Description of the Drawings

[0014] [Figure 1] Figure 1 shows the internal torque and temperature in the reactor of Examples 1-2. [Figure 2] Figure 2 shows the internal torque and temperature in the reactor of Comparative Examples 1-3. [Figure 3] Figure 3 shows the internal torque and temperature in the reactor of Reference Example 1-1. [Figure 4] Figure 4 shows the internal torque and temperature in the reactor of Reference Example 1-2. [Figure 5] Figure 5 shows the internal torque and temperature in the reactor of Reference Example 1-3. [Figure 6] Figure 6 shows the 1H NMR spectrum of the carboxymethylated starch produced in Example 1-1. [Figure 7] Figure 7 shows the 1H NMR spectrum of the carboxymethylated starch produced in Example 1-2. [Figure 8] Figure 8 shows the 1H NMR spectrum of the carboxymethylated starch produced in Reference Example 1-1. [Figure 9] Figure 9 shows the 1H NMR spectrum of the carboxymethylated starch produced in Reference Example 1-2. [Figure 10]Figure 10 shows the 1H NMR spectra of the carboxymethylated starch produced in Reference Examples 1-3.

BEST MODE FOR CARRYING OUT THE INVENTION

[0015] The terms used in this specification are used only for explaining exemplary embodiments and are not intended to limit the invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In this specification, terms such as "including", "comprising", or "having" are intended to specify the presence of implemented features, steps, components, or combinations thereof, and should not be construed as precluding the presence or addition of one or more other features, steps, components, or combinations thereof.

[0016] Also, in the present invention, when it is mentioned that each layer or element is formed "on" or "above" each layer or element, it means that each layer or element is formed directly on each layer or element, or that other layers or elements may be additionally formed between each layer, on the object, or on the substrate.

[0017] The present invention can be subject to various modifications and can have various forms, so specific embodiments are exemplified and described in detail below. However, this is not intended to limit the present invention to a specific disclosed form, and it should be understood to include all modifications, equivalents, or alternatives included in the spirit and technical scope of the present invention.

[0018] Also, the technical terms used in this specification are for referring to specific embodiments only and are not intended to limit the present invention. And the singular forms used here include plural forms unless the context clearly indicates the contrary meaning.

[0019] On the other hand, conventionally used superabsorbent polymers are manufactured by polymerizing acrylic acid monomers together with a crosslinking agent in the presence of a polymerization initiator. However, superabsorbent polymers manufactured in this way are not biodegradable, which causes environmental problems.

[0020] Therefore, development is underway to create superabsorbent polymers that can exhibit biodegradability. Materials such as polysaccharides, polyaspartic acid, and polyglutamic acid have been cited as biodegradable materials that can be used to produce such polymers. However, these materials reduce the absorption capacity, which is an important property of superabsorbent polymers, and mass production is not easy. As a result, it has been difficult to replace superabsorbent polymers made from acrylic acid monomers.

[0021] For this reason, modified polysaccharides, which are readily available and biodegradable, such as starch, have been used by introducing various functional groups into them. However, the organic solvents used in the production of such modified polysaccharides are environmentally unfriendly and economically unviable.

[0022] Therefore, the inventors have confirmed that when a polysaccharide such as starch is gelatinized while being stirred with a small amount of water, a rotational force (torque) is induced within the polysaccharide. When the carboxyalkylation reaction is carried out under such a torque above a certain level, the reaction can be carried out in a short time without the additional use of an alcohol-based solvent, and the reaction efficiency (reactive efficiency, RE) can be increased compared to when an additional alcohol-based solvent is used. Based on these findings, the inventors have completed the present invention.

[0023] Furthermore, the inventors confirmed that when the carboxyalkylated polysaccharide produced as described above is self-crosslinked under specific pH conditions without the use of an internal crosslinking agent, a biodegradable superabsorbent resin exhibiting high absorption performance can be produced. The following describes each invention in detail.

[0024] The following describes each invention in detail.

[0025] (Method for producing carboxyalkylated polysaccharides) A method for producing carboxyalkylated polysaccharides with improved reaction efficiency (RE) includes the step of mixing polysaccharides, hydroxides, metal salts of haloalkylcarboxylic acids, and water in a reactor to carry out the gelatinization and carboxyalkylation reactions of the polysaccharides. At this time, the amount of water used is 0.35 to 1.0 times the weight of the polysaccharides, and the torque in the reactor is maintained at 7 to 18 Nm after the gelatinization of the polysaccharides.

[0026] More specifically, in the above step, the polysaccharide is first gelatinized by mixing it with hydroxide and water, and then the gelatinized polysaccharide is subjected to a carboxyalkylation reaction with a metal salt of a haloalkylcarboxylic acid.

[0027] In this case, the point at which the gelatinization of the polysaccharide is completed can be confirmed by measuring the internal torque in the reactor from the start of mixing to the completion of mixing using a torque measuring sensor installed in the reactor, and determining when the torque stabilizes. More specifically, when a polysaccharide is gelatinized with water and hydroxide, the internal thermal energy increases due to the load induced during the gelatinization process, causing the torque and temperature to increase. After the torque and temperature in the reactor are maintained constant once gelatinization is complete. Therefore, the carboxyalkylation reaction of the polysaccharide may be carried out under constant torque conditions in the reactor, which makes it possible to produce carboxyalkylated polysaccharides with a uniform degree of substitution and improved substitution efficiency.

[0028] Therefore, if the torque inside the reactor is less than 7 Nm after the gelatinization of the polysaccharide, there is a problem that the substitution efficiency of carboxyalkyl groups will decrease. If the torque exceeds 18 Nm, the internal temperature will increase excessively, causing the water used as a solvent to evaporate, which may reduce workability and is undesirable.

[0029] More specifically, the torque (Nm) in the above step may be 7 or more, 7.5 or more, or 8 or more, and 18 or less, 16 or less, 15 or less, 14 or less, 13 or less, 12 or less, 11 or less, 10 or less, or 9 or less.

[0030] The aforementioned polysaccharides refer to polymeric carbohydrate molecules consisting of glucose repeating units, and in this case, polymeric molecules consisting of glucosamine repeating units in which an amino group is introduced to the hydroxyl group bonded to the second carbon atom in the glucose repeating unit, and / or N-acetylglucosamine repeating units in which an N-acetylamino group is introduced to the hydroxyl group bonded to the second carbon atom in the glucose repeating unit. Such polysaccharides can be classified into storage polysaccharides used as a general energy source, structural polysaccharides that form structural components of plants and animals such as plant cell walls and arthropod exoskeletons, or capsular polysaccharides that form the capsules of bacteria. Examples of storage polysaccharides include starch, dextrin, glycogen, and inulin; examples of structural polysaccharides include cellulose, chitin, chitosan, pectin, arabinoxylan, carrageenan, and agar; and examples of capsule polysaccharides include alginate, xanthan gum, guar gum, gellan gum, dextran, and welan gum. Of these, those that can be gelatinized are suitable for the method of producing the carboxyalkylated polysaccharides. More specifically, the polysaccharides that can be used include starch, dextrin, glycogen, inulin, cellulose, chitosan, pectin, agar, carrageenan, alginate, xanthan gum, guar gum, gellan gum, or combinations thereof.

[0031] Here, gelatinization of polysaccharides refers to the phenomenon in which the physical properties of polysaccharide particles change through hydration, swelling, and disintegration processes when polysaccharides are heated with water or mixed with water and a base. More specifically, the micelle structure within the polysaccharide particles absorbs water molecules, causing the polysaccharide particles to swell, and then the micelle structure within the polysaccharide particles disintegrates due to thermal energy or the base. In other words, in the above manufacturing method, hydroxides, which are bases that promote such gelatinization, are used together with the polysaccharides, and a small amount of water is used compared to the polysaccharides. Therefore, a turning force is induced during the gelatinization process, and thermal energy is continuously supplied to the polysaccharides, thus further promoting gelatinization.

[0032] Therefore, in the above manufacturing method, the polysaccharide that can be gelatinized may not have any reactive functional groups other than the hydroxyl group. For example, it is preferable that one or more selected from the group consisting of starch, dextrin, glycogen, inulin, cellulose, pectin, agar, and guar gum be used as the polysaccharide. More preferably, dextrin, which is a hydrolysate of starch or starch, can be used as the polysaccharide.

[0033] In particular, starch is preferred because it is readily available and can be found in large quantities in foods and beverages such as potatoes, wheat, corn, rice, and tapioca. Such starches contain amylose and amylopectin, and the amylose and amylopectin may be present in the starch in a weight ratio of 1:99 to 80:20. This is because it is advantageous in terms of processability and solubility for the amylopectin content to be greater than or equal to the amylose content. Such starches can be selected from potato starch, corn starch, rice starch, wheat starch, tapioca starch, and sweet potato starch, and potato starch, which has a higher amylopectin content, may be more preferred.

[0034] Furthermore, the gelatinized polysaccharide produced in the above steps is not in a fluid liquid state dissolved in water or suspended, but rather in a semi-solid gel state. Since this gel-like gelled polysaccharide is mixed by the two screws and the shear action of the chamber wall provided in the reactor, the torque and thermal energy inside the reactor can be maintained above a certain level.

[0035] To maintain a torque value above a certain level after the gelatinization of such polysaccharides, controlling the amount of water used is crucial. Therefore, in order to maintain torque so that the carboxyalkylation reaction in the reactor proceeds smoothly, while simultaneously producing carboxyalkylated polysaccharides with a uniform degree of substitution, water needs to be used in an amount of 0.35 to 1.0 times the weight of the polysaccharide.

[0036] In contrast, when water is used in amounts less than 0.35 times the weight of the polysaccharide, the increased torque during the gelatinization process of the polysaccharide causes the water to evaporate, leading to problems with workability and difficulty in producing carboxyalkylated polysaccharides with a uniform degree of substitution. Furthermore, when water is used in amounts exceeding 1.0 times the weight of the polysaccharide, the torque during the gelatinization process decreases, reducing reaction efficiency and yield. This not only increases the cost of drying the water but also increases the amount of by-products such as sodium chloride (NaCl) produced during the reaction process, potentially reducing the absorption performance of the superabsorbent polymer, which is undesirable.

[0037] More specifically, the water can be used in an amount of 0.35 times or more, 0.4 times or more, 0.45 times or more, 0.5 times or more, 0.6 times or more, or 0.7 times or more relative to the weight of the polysaccharide, and in an amount of 1.0 times or less, 0.9 times or less, 0.8 times or less, 0.75 times or less, 0.74 times or less, 0.73 times or less, or 0.72 times or less.

[0038] Preferably, the water can be used in an amount equal to 0.45 to 0.75 times the weight of the polysaccharide.

[0039] Furthermore, the water can be any ordinary water, such as tap water, distilled water, deionized water, or purified water, without any restrictions, but distilled water is preferable.

[0040] Furthermore, the hydroxide and the metal salt of the haloalkylcarboxylic acid are not soluble in water before being mixed with the polysaccharide. Also, unlike conventional methods, the polysaccharide is not mixed with an organic solvent before being mixed with the hydroxide. Instead, in this method, all the reactants for the carboxyalkylation reaction are introduced into the reactor along with the solvent, thus improving manufacturing efficiency by shortening the manufacturing process.

[0041] Furthermore, when the polysaccharides are mixed with hydroxides, metal salts of haloalkylcarboxylic acids, and water, no solvents other than water are used. Examples of other solvents commonly used besides water include alcohol-based solvents such as ethanol, methanol, or isopropyl alcohol, and solvents that are miscible with water, such as acetone, 1,4-dioxane, dimethylformamide, and dimethyl sulfoxide.

[0042] If water is not used at all as a solvent for the gelatinization and carboxyalkylation reactions of polysaccharides, the hydroxide and metal salts of haloalkylcarboxylic acids do not mix well with the polysaccharides, resulting in a failure of the reaction to proceed. If other solvents are mixed with water, environmental problems and recovery costs may arise, and safety issues may arise due to evaporation because of the low boiling point. Furthermore, if other solvents are mixed with water in the reactor, they may hinder the gelatinization of the polysaccharides, causing them to solidify and creating mixing problems. However, in the above-described manufacturing method, these problems can be overcome by using only water as the solvent for the gelatinization and carboxyalkylation reactions of polysaccharides.

[0043] On the other hand, the polysaccharide used in the above manufacturing method contains anhydroglucose units (AGU) represented by the following chemical formula 1, and the molecular weight of the anhydroglucose units (AGU) is 162.14. [ka]

[0044] In the aforementioned chemical formula 1, the numbering refers to the position of each carbon, and carboxyalkylation can occur at the hydroxyl group of the second (C2), third (C3), or sixth (C6) carbon in the anhydrous glucose unit (AGU). For example, in carboxymethylated polysaccharides, one or more hydroxyl groups (OH) in the anhydrous glucose unit (AGU) are converted into carboxymethyl groups (OCH2COOH / OCH2COOH). - It has a structure that is replaced by ).

[0045] Therefore, as an example, when using an alkali metal salt of haloacetic acid as the metal salt of a haloalkylcarboxylic acid, the carboxyalkylated polysaccharide finalized through the above manufacturing method will contain carboxymethylated glucose units represented by the following chemical formula 2. [ka]

[0046] In the aforementioned chemical formula 2, R is independently hydrogen and CH2COO - M + , or CH2COOH, However, at least one of R is CH2COO - M + , or CH2COOH, where M represents an alkali metal.

[0047] The degree of substitution (DS) of the carboxyalkyl group in the carboxyalkylated polysaccharide produced by this manufacturing method may be 0.6 to 1.1. If the degree of substitution (DS) of the carboxyalkyl group is excessively low, it may not dissolve sufficiently in the water dissolution process necessary for the production of superabsorbent polymers, resulting in a decrease in the water retention capacity of the superabsorbent polymer. If the degree of substitution (DS) of the carboxyalkyl group is excessively high, it is undesirable because it leads to the generation of many by-reactants, reducing the reaction efficiency and biodegradability efficiency.

[0048] More specifically, the degree of substitution (DS) of the carboxyalkyl group may be 0.6 or higher, 0.62 or higher, or 0.64 or higher, and may also be 1.1 or lower, 1.05 or lower, 1.0 or lower, 0.96 or lower, 0.9 or lower, 0.8 or lower, 0.7 or lower, or 0.65 or lower.

[0049] Here, the degree of substitution of carboxyalkyl groups (DS) refers to the average number of hydroxyl groups (-OH) substituted for carboxyalkyl groups per repeating unit of anhydrous glucose. In other words, since there are 3 hydroxyl groups per repeating unit of glucose, the theoretical maximum degree of substitution is 3, and a degree of substitution of 0.1 means that 3 hydroxyl groups are substituted for 10 repeating units of glucose. Furthermore, the degree of substitution of such acidic groups is the same as that of the carboxyalkylated polysaccharide produced in the final product. 1 This can be calculated through 1H NMR analysis.

[0050] In this case, the carboxyalkylated polysaccharide may also be carboxymethylated. Thus, the degree of substitution (DS) of the carboxyalkyl group in the carboxyalkylated polysaccharide can be considered to represent the degree of substitution of the carboxymethyl group in the carboxymethylated polysaccharide.

[0051] Furthermore, the hydroxide may be one or more selected from the group consisting of sodium hydroxide, potassium hydroxide, and lithium hydroxide. In this case, sodium hydroxide (NaOH) is most preferred in terms of availability.

[0052] Furthermore, the hydroxide can be used in an equivalent amount of 0.5 to 1.5 relative to the number of moles obtained by dividing the weight (g) of the polysaccharide by the molecular weight of anhydrous glucose units (AGU). Specifically, the equivalent amount of hydroxide to be used can be determined by first finding the number of moles by dividing the weight (g) of the hydroxide used by the molecular weight, and then dividing the resulting number of moles of hydroxide by the number of moles of the polysaccharide obtained by dividing the weight (g) of the polysaccharide used by the molecular weight of anhydrous glucose units (AGU), which is 162.14.

[0053] More preferably, the hydroxide can be used in an equivalent amount of 0.5 or more and less than 1.2 relative to the number of moles obtained by dividing the weight (g) of the polysaccharide by the molecular weight of anhydrous glucose units (AGU). If the equivalent amount of hydroxide used is excessively low, the reaction may not proceed due to insufficient hydroxide, resulting in a low degree of carboxyalkyl substitution in the final carboxyalkylated polysaccharide. If the equivalent amount of hydroxide used is excessively high, a process to neutralize the high pH with unreacted hydroxide becomes necessary, which may result in the generation of by-products that reduce absorption capacity.

[0054] More specifically, the hydroxide can be used in an equivalent amount of 0.5 or more, 0.6 or more, or 0.7 or more relative to the number of moles obtained by dividing the weight (g) of the polysaccharide by the molecular weight of anhydrous glucose units (AGU), and 1.15 or less, 1.1 or less, 1.0 or less, 0.9 or less, or 0.8 or less.

[0055] Furthermore, the metal salt of the haloalkylcarboxylic acid refers to a metal salt of an alkylcarboxylic acid (alkylcarboxylic acid, alkanoic acid, R-COOH, where R is alkyl) having at least one halogen substituent; in other words, it means a compound in which the anion of an alkylcarboxylic acid having at least one halogen substituent is ionically bonded to a metal cation. Here, the metal salt may be an alkali metal salt, an alkaline earth metal salt, or a two-phase transition metal salt. The halogen substituent may preferably be chloro or bromo. The alkyl group may be linear or branched, and its carbon number is not particularly limited, but may be 1 to 20 or 1 to 10. Specific examples of the alkyl groups include methyl, ethyl, propyl, n-propyl, isopropyl, butyl, n-butyl, isobutyl, tert-butyl, sec-butyl, 1-methyl-butyl, 1-ethylbutyl, pentyl, n-pentyl, isopentyl, neopentyl, tert-pentyl, 1-ethyl-propyl, 1,1-dimethylpropyl, hexyl, n-hexyl, 1-methylpentyl, 2-methylpentyl, 4-methyl-2-pentyl, 3,3-dimethylbutyl, and 2-ethylbutyl. Examples include, but are not limited to, heptyl, n-heptyl, isohexyl, 1-methylhexyl, 2-methylhexyl, 3-methylhexyl, 4-methylhexyl, 5-methylhexyl, cyclopentylmethyl, cyclohexylmethyl, octyl, n-octyl, tert-octyl, 1-methylheptyl, 2-ethylhexyl, 2,4,4-trimethyl-1-pentyl, 2,4,4-trimethyl-2-pentyl, 2-propylpentyl, n-nonyl, and 2,2-dimethylheptyl.

[0056] Such metal salts of haloalkylcarboxylic acids may also be alkali metal salts of haloalkylcarboxylic acids.

[0057] In one example, if the carboxyalkylated polysaccharide is carboxymethylated, the metal salt of the haloalkylcarboxylic acid may be an alkali metal salt of haloacetic acid.

[0058] In another embodiment, the metal salt of the haloalkyl carboxylic acid may be an alkali metal salt of an alkyl carboxylic acid substituted with at least one chloro.

[0059] In yet another embodiment, the metal salt of the haloalkyl carboxylic acid may be an alkali metal salt of acetic acid substituted with at least one chloro. <00,00248> Preferably, considering the reactivity, the metal salt of the haloalkyl carboxylic acid may be an alkali metal salt of chloroacetic acid.

[0061] The alkali metal salt of chloroacetic acid may be one or more selected from the group consisting of sodium monochloroacetate (SMCA), potassium monochloroacetate, and lithium monochloroacetate. Preferably, sodium monochloroacetate (SMCA) is used considering the ease of availability and reactivity.

[0062] As an example, when sodium monochloroacetate is used as the metal salt of the haloalkyl carboxylic acid, the finally produced carboxymethylated polysaccharide will contain a repeating unit represented by the following Chemical Formula 2-1.

Chemical Formula

[0063] In Chemical Formula 2-1, each R1 is independently hydrogen, CH2COO - Na + , or CH2COOH, provided that at least one of R1 is CH2COO - Na + , or CH2COOH.

[0064] In this case, the metal salt of the haloalkylcarboxylic acid can be used in an amount of 0.5 to 1.5 equivalents relative to the number of moles obtained by dividing the weight (g) of the polysaccharide by the molecular weight of anhydrous glucose units (AGU). Specifically, the equivalent amount of the metal salt of the haloalkylcarboxylic acid to be used can be determined by first finding the number of moles by dividing the weight (g) of the metal salt of the haloalkylcarboxylic acid used by its molecular weight, and then dividing the obtained number of moles of the metal salt of the haloalkylcarboxylic acid by the number of moles of the polysaccharide obtained by dividing the weight (g) of the polysaccharide used by the molecular weight of anhydrous glucose units (AGU), which is 162.14.

[0065] More preferably, the metal salt of the haloalkylcarboxylic acid can be used in an equivalent amount of 0.5 or more and less than 1.2 relative to the number of moles obtained by dividing the weight (g) of the polysaccharide by the molecular weight of anhydrous glucose units (AGU). If the content of the metal salt of the haloalkylcarboxylic acid is excessively low, there is a problem that the hydroxyl groups of the polysaccharide are not sufficiently substituted with carboxymethyl groups. If the content of the metal salt of the haloalkylcarboxylic acid is excessively high, chloroacetic acid or glycolic acid may be formed as a byproduct of side reactions that occur during the reaction, and the reaction efficiency of producing carboxymethylated polysaccharides in the neutralization reaction with hydroxide may actually decrease. In addition, if the pH decreases due to the neutralization reaction, a crosslinking reaction may also occur during the reaction, which may reduce the absorption capacity.

[0066] More specifically, the metal salt of the haloalkylcarboxylic acid can be used in an amount of 0.5 or more, 0.6 or more, or 0.7 or more relative to the number of moles obtained by dividing the weight (g) of the polysaccharide by the molecular weight of anhydrous glucose units (AGU), and in an equivalent amount of 1.15 or less, 1.1 or less, 1.0 or less, 0.9 or less, or 0.8 or less.

[0067] Furthermore, the metal salt of the haloalkylcarboxylic acid can be used in an amount of 1 mole to 1.29 moles per mole of the hydroxide. If the metal salt of the haloalkylcarboxylic acid is used in an excessively large or excessively small amount compared to the hydroxide, the carboxyalkyl group substitution reaction may not proceed sufficiently to achieve the degree of substitution (DS) of the carboxyalkyl group within the range described above, which may increase the content of sodium chloride (NaCl), a byproduct that may be generated during the reaction. In addition, the overproduction of the haloalkylcarboxylic acid or glycolic acid may lead to the formation of partially cross-linked structures. More specifically, the metal salt of the haloalkylcarboxylic acid and the hydroxide can be used in a 1:1 molar ratio.

[0068] Furthermore, the mixing may be carried out when the reactor is filled to 70 to 95% of its total volume. If the total volume of reactants filled in the reactor is excessively small, the torque may not increase sufficiently during gelatinization for the carboxyalkylation reaction to occur. If the total volume of reactants filled in the reactor is excessively large, there is a disadvantage that it may be difficult to introduce the reactants into the reactor, resulting in an uneven carboxyalkylation substitution reaction.

[0069] More specifically, the mixing may be carried out when the reactor is filled to 70% or more, 75% or more, 76% or more, or 77% or more of the total volume, and 95% or less, 94% or less, 93% or less, or 92% or less.

[0070] Furthermore, any kneader equipped with two screws or rotor blades capable of inducing torque and thermal energy can be used as a reactor for the production of the aforementioned carboxyalkylated polysaccharides. Examples include internal mixers such as the Banbury mixer and Intermix mixer, and two-roll mills.

[0071] Preferably, an internal mixer can be used as the reactor.

[0072] Furthermore, the mixing may be carried out for 5 to 15 minutes. During this time, the two screws or rotors with blades provided in the reactor may be rotated at 30 to 100 rpm. More preferably, the mixing may be carried out for 10 minutes.

[0073] Here, the gelatinization of the polysaccharide can be completed in less than 2 / 5 of the total mixing time from the start of mixing. The point at which the gelatinization of the polysaccharide is completed can be confirmed when the internal torque in the reactor stabilizes, by measuring the internal torque in the reactor from the start of mixing to the completion of mixing using temperature and torque measuring sensors provided in the reactor, as described above. For example, if the total mixing time is 10 minutes, the gelatinization of the polysaccharide can be completed within 4 minutes.

[0074] On the other hand, the temperature inside the reactor may be maintained at 90 to 110°C after the gelatinization of the polysaccharide. This is because the internal temperature inside the reactor rises until the completion of gelatinization due to the increase in internal thermal energy caused by the load induced during the gelatinization process, but since no additional load is induced after the completion of gelatinization, a certain temperature range is maintained. Therefore, by maintaining not only the torque but also the temperature above a certain level after the gelatinization of the polysaccharide, the substitution efficiency of the carboxyalkyl group of the polysaccharide can be further improved.

[0075] More specifically, after the gelatinization of the polysaccharide, the temperature inside the reactor may be 90°C or higher, 92°C or higher, 94°C or higher, or 96°C or higher, and 110°C or lower, 105°C or lower, 100°C or lower, less than 100°C, 99°C or lower, 98°C or lower, or 97°C or lower.

[0076] Furthermore, when an internal mixer is used as the reactor, as described above, the temperature and torque inside the reactor can be measured through temperature and torque measuring sensors between the two screws.

[0077] Furthermore, the manufacturing method may further include a step of dissolving the manufactured product in water and then precipitating it in an alcoholic organic solvent. This is to purify the manufactured carboxyalkylated polysaccharide to obtain a carboxyalkylated polysaccharide from which impurities have been removed.

[0078] Here, the alcoholic organic solvent may be one or more selected from the group consisting of methanol, ethanol, and isopropyl alcohol.

[0079] Furthermore, the alcohol-based organic solvent can be used in an amount (ml / g) that is 10 to 60 times the volume of the produced product. Of these, methanol is most preferred considering purification efficiency and cost.

[0080] Furthermore, the manufacturing method may further include, after the above step, a step of collecting the precipitate by vacuum filtration and a step of drying the collected precipitate. Through this, a carboxyalkylated polysaccharide can be obtained from which the remaining hydroxide and generated by-products have been effectively removed.

[0081] (Method for producing biodegradable superabsorbent polymers) A method for producing a biodegradable superabsorbent polymer with improved water retention capacity includes the following steps.

[0082] Step 1 involves dissolving the carboxyalkylated polysaccharide produced by the manufacturing method described above in 5 to 15 times the weight of the carboxyalkylated polysaccharide in water, Step 2 involves drying the product from Step 1 under pH 6 to 8 conditions while allowing it to self-crosslink.

[0083] Step 1 First, step 1 is the step of dissolving the carboxyalkylated polysaccharide produced by the manufacturing method described above in 5 to 15 times the weight of the carboxyalkylated polysaccharide in water, thereby ensuring that self-crosslinking in step 2, described later, occurs sufficiently in the solution.

[0084] Here, if the carboxyalkylated polysaccharide is dissolved in less than five times the weight of the polysaccharide in water, the precipitate will solidify, causing problems in removing by-products. If the carboxyalkylated polysaccharide is dissolved in more than 15 times the weight of the polysaccharide in water, there may be problems with increased costs due to excessive use of the solvent.

[0085] The dissolution in step 1 may be carried out under normal temperature and atmospheric pressure conditions. Here, normal temperature means a temperature of about 21 to 23°C, and atmospheric pressure means atmospheric pressure without any added pressure.

[0086] Step 2 Step 2 is a step in which the product of Step 1 is self-crosslinked while being dried under pH 6 to 8 conditions, the pH of which can be adjusted, for example, through an aqueous hydrochloric acid solution, an aqueous sodium hydroxide solution, or an aqueous potassium hydroxide solution, but is not limited to these, and can be adjusted using an acid / base solution commonly used to adjust pH. Through this step, a crosslinked polymer is produced in which polysaccharides are crosslinked by an esterification reaction within the carboxyalkylated polysaccharides.

[0087] In particular, the crosslinking reaction in step 2 is a self-crosslinking reaction, and does not use crosslinking agents that are typically used in the production of crosslinked polymers of superabsorbent polymers. More specifically, while meth(acrylate) compounds such as polyethylene glycol (meth)acrylate and ethylene glycol di(meth)acrylate, and epoxy compounds such as ethylene glycol diglycidyl ether, propylene glycol, and glycerin are typically used as crosslinking agents, such crosslinking agents are not used in the above production method. If a crosslinking agent were to be used, the amount of biomass-based raw materials in the final superabsorbent polymer would decrease, so self-crosslinking of carboxyalkylated polysaccharides without a separate crosslinking agent is advantageous for improving biodegradability.

[0088] Furthermore, a reaction catalyst and / or thermal stabilizer can be used to promote such esterification reactions during the crosslinking reaction.

[0089] As the esterification reaction catalyst, 4-dimethylaminopyridine (DMAP), magnesium acetate, tetra-n-butyl titanate (TBT), lead acetate, sodium acetate, potassium acetate, antimony trioxide, N-methylimidazole, or a combination thereof can be used. The catalyst can be used in an amount of 0.1 to 5 moles per mole of carboxyalkylated polysaccharide to shorten the reaction time and obtain the desired degree of crosslinking. Specifically, the reaction catalyst can be used in an amount of 0.1 mole or more, 0.5 mole 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 carboxyalkylated polysaccharide.

[0090] Furthermore, organic or inorganic phosphorus compounds can be used as the heat stabilizer. 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 phosphates, or aryl phosphates can be used as the heat stabilizer.

[0091] Furthermore, during the crosslinking reaction, additives such as thickeners, plasticizers, storage stabilizers, and antioxidants may be used as needed.

[0092] Furthermore, the self-crosslinking reaction in step 2 is carried out under pH conditions of 6 to 8. If the pH during the self-crosslinking reaction is less than 6, the crosslinking reaction may proceed too rapidly, potentially reducing the water retention capacity of the superabsorbent polymer. If the pH during the self-crosslinking reaction exceeds 8, the crosslinking may proceed too slowly or the reaction may hardly occur at all, making it unsuitable.

[0093] Furthermore, drying in step 2 may be carried out at a temperature of 100 to 130°C. The drying method can be selected and used without limiting its configuration, as long as it is a commonly used method. Specifically, the drying step can be carried out by methods such as hot air supply, infrared irradiation, ultra-high frequency irradiation, or ultraviolet irradiation.

[0094] Specifically, the drying may be carried out under vacuum conditions. On the other hand, the drying time may be approximately 30 minutes to approximately 4 hours, or approximately 2 to approximately 3 hours, taking into consideration process efficiency and other factors.

[0095] Furthermore, the drying method can be selected and used without limitation, as long as it is one that is normally used in the production of superabsorbent polymers. Specifically, the drying step can be carried out by methods such as hot air supply, infrared irradiation, ultra-high frequency irradiation, or ultraviolet irradiation. The water content of the crosslinked polymer produced after such drying may be about 5 to about 10% by weight.

[0096] Additional steps Furthermore, the manufacturing method may further include, after step 2, a step of grinding and classifying the crosslinked polymer produced in step 2.

[0097] However, a coarse grinding step may be selectively performed before the grinding of the crosslinked polymer.

[0098] The aforementioned coarse grinding step is a step to improve drying efficiency in the subsequent drying step and to control the particle size of the superabsorbent polymer powder finally produced. The grinder used in this step is not limited in its configuration, but specifically, one of the grinding equipment consisting of a vertical pulverizer, turbo cutter, turbo grinder, rotary cutter mill, cutter mill, disc mill, shred crusher, crusher, meat chopper, and disc cutter may be selected.

[0099] Furthermore, the coarse grinding step may be carried out, for example, so that the weight-average particle size of the crosslinked polymer is about 2 to about 10 mm. Grinding the crosslinked polymer to a particle size of less than 2 mm is technically difficult due to the high water content of the crosslinked polymer, and a phenomenon of aggregation between the ground particles may occur. On the other hand, if the particle size is ground to more than 10 mm, the effect of increasing the efficiency of the subsequent drying step may be reduced.

[0100] Next, the coarsely ground crosslinked polymer may be ground and classified.

[0101] The grinding process may be carried out so that the particle size of the crosslinked polymer powder, i.e., the base resin, is about 150 to about 850 μm. The grinders used to grind to such particle size can specifically include pin mills, hammer mills, screw mills, roll mills, disc mills, or jog mills, but the present invention is not limited to the examples described above.

[0102] Furthermore, after the grinding step described above, a further step may be taken to classify the ground cross-linked polymer powder according to its particle size in order to control the physical properties of the superabsorbent polymer that will be used as the final product.

[0103] As a result, the superabsorbent polymer produced can be in powder form with a particle size of 150 to 850 μm. Such particle size can be measured by the European Disposables and Nonwovens Association (EDANA) standard EDANA WSP 220.3 method.

[0104] Furthermore, the superabsorbent polymer can satisfy a centrifugal water retention capacity (CRC) of 30 to 45 g / g, as measured by the EDANA method WSP 241.3. More specifically, the centrifugal water retention capacity (CRC) of the superabsorbent polymer may be 30 g / g or more, 35 g / g or more, 37 g / g or more, 39 g / g or more, 39.2 g / g or more, 40 g / g or more, 41 g / g or more, or 41.2 g / g or more, and 45 g / g or less, 44 g / g or less, or 43.5 g / g or less.

[0105] The present invention will be described in more detail below with reference to the following examples. However, the following examples are for illustrative purposes only, and the scope of the present invention is not limited to these examples. [Examples]

[0106] Example - Production of carboxymethylated starch Measurement of the moisture content of potato starch The moisture content of potato starch is the amount of water relative to the total weight of the potato starch obtained. It can be calculated as a percentage obtained by subtracting the weight of the dry potato starch from the total weight of the potato starch and dividing the result by the total weight of the potato starch. In this case, the weight of the dry potato starch is determined using a Moisture Analyzer, measuring the value when the weight change is within 0.001 g and does not change for 30 seconds or more during drying at 125°C. Using the above method, the moisture content of the potato starch used in the examples, comparative examples, and reference examples was measured to be 17% by weight, which indicates that the actual starch content in the potato starch is 83% by weight.

[0107] Example 1-1 In an internal mixer reactor, 28 g of potato starch (manufactured by DAESANG, moisture content 17% by weight) (actual starch content considering moisture content: 23.24 g, 0.143 mol), 4.01 g of NaOH (0.1 mol, 0.7 equivalents relative to the number of starch moles), 11.69 g of SMCA (0.1 mol, 0.7 equivalents relative to the number of starch moles), and 12 g of distilled water were packed to 77% of the reactor volume, and mixed at 50 rpm for 10 minutes to carry out the gelatinization and carboxymethylation reactions of starch.

[0108] At this time, the internal torque and temperature inside the reactor during mixing were measured using temperature and torque measuring sensors located between the two screws provided in the internal mixer reactor. The measurement results confirmed that starch gelatinization was completed within 3 minutes from the start of mixing, and that the torque and temperature inside the reactor were maintained at 7 to 9 Nm and 96.3 ± 1 °C, respectively, after starch gelatinization.

[0109] After recovering the manufactured carboxymethyl starch, it was dissolved in distilled water and precipitated in methanol in an amount 40 times the volume of the carboxymethyl starch (ml / g). The purified carboxymethylated starch was then obtained by vacuum filtration and drying.

[0110] Examples 1-2 (Step 1) 33.4 g of potato starch (manufactured by DAESANG, moisture content 17% by weight) (actual starch content considering moisture content: 27.72 g, 0.171 mol), 4.79 g of NaOH (0.12 mol, 0.7 equivalents relative to the number of starch moles), 13.94 g of SMCA (0.12 mol, 0.7 equivalents relative to the number of starch moles), and 14.31 g of distilled water were packed into an internal mixer reactor to 92% of the reactor volume, and mixed at 50 rpm for 10 minutes to carry out the gelatinization and carboxymethylation reactions of starch.

[0111] At this time, the internal torque and temperature inside the reactor during mixing were measured using temperature and torque measuring sensors located between the two screws of the internal mixer reactor, and the graph of these measurements is shown in Figure 1. The measurement results confirmed that starch gelatinization was completed within 3 minutes from the start of mixing, and that the torque and temperature inside the reactor were maintained at 8 to 10 Nm and 96.4 ± 1°C, respectively, after starch gelatinization.

[0112] Subsequently, an additional purification step was performed in the same manner as in Example 1-1 to obtain purified carboxymethylated starch.

[0113] Comparative Example 1-1 200 L of isopropyl alcohol (IPA) was placed in a flask, and 20 g of potato starch (manufactured by DAESANG, moisture content 17% by weight) (actual starch content considering moisture content: 16.60 g, starch content 0.102 mol) and 4.34 g of NaOH (0.109 mol, 1.06 equivalents relative to the number of starch moles) were dispersed therein, and the temperature was maintained at 70°C. Then, 20 g of distilled water and 12.65 g of SMCA (0.109 mol, 1.06 equivalents relative to the number of starch moles) were added and the mixture was reacted for 5 hours to produce carboxymethylated starch. In this case, as in Comparative Example 1-1, the gelatinization and carboxymethylation reactions of starch occurred in the flask with an excess of solvent, so sufficient torque was not induced in the flask.

[0114] Next, purified carboxymethylated starch was obtained by performing an additional purification step in the same manner as in Example 1-1.

[0115] Comparative Example 1-2 400 L of isopropyl alcohol (IPA) was added to a flask, and 200 g of potato starch (manufactured by DAESANG, moisture content 17% by weight) (actual starch content considering moisture content: 166 g, 1.02 mol) and 30.71 g of NaOH (0.768 mol, 0.75 equivalents relative to the number of starch moles) were dispersed therein, and the temperature was maintained at 70°C. Then, 77 g of distilled water and 89.44 g of SMCA (0.768 mol, 0.75 equivalents relative to the number of starch moles) were added and the mixture was reacted for 5 hours to produce carboxymethylated starch. In the case of Comparative Examples 1-2, the gelatinization and carboxymethylation reactions of starch occurred in the flask, so sufficient torque was not induced in the flask.

[0116] Next, purified carboxymethylated starch was obtained by performing an additional purification step in the same manner as in Example 1-1.

[0117] Comparative Examples 1-3 In an internal mixer reactor, 28 g of potato starch (manufactured by DAESANG, moisture content 17% by weight) (actual starch content considering moisture content: 23.24 g, 0.143 mol), 6.91 g of NaOH (0.173 mol, 1.2 equivalents relative to the number of starch moles), 20.11 g of SMCA (0.173 mol, 1.2 equivalents relative to the number of starch moles), 3 g of distilled water, and 9 g of IPA were packed to 95% of the reactor volume, and the mixture was mixed at 50 rpm for 10 minutes to carry out the gelatinization and carboxymethylation reactions of starch.

[0118] At this time, the internal torque and temperature inside the reactor during mixing were measured through temperature and torque measuring sensors located between the two screws of the internal mixer reactor, and the graph of these measurements is shown in Figure 2. The measurement results confirmed that starch gelatinization was completed within 3 minutes from the start of mixing, and that after starch gelatinization, the torque inside the reactor continuously rose to 90 Nm or more and the temperature rose to 130°C or more. As a result, the carboxymethylation reaction did not proceed easily, and carboxymethylated starch with a uniform degree of substitution could not be obtained.

[0119] Reference Example 1-1 28 g of potato starch (manufactured by DAESANG, moisture content 17% by weight) (actual starch content considering moisture content: 23.24 g, 0.143 mol), 6.91 g of NaOH (0.173 mol, 1.2 equivalents relative to the number of starch moles), 20.11 g of SMCA (0.173 mol, 1.2 equivalents relative to the number of starch moles), and 12 g of distilled water were packed into an internal mixer reactor to 90% of the reactor volume, and mixed at 50 rpm for 10 minutes to carry out the gelatinization and carboxymethylation reactions of starch.

[0120] At this time, the internal torque and temperature inside the reactor during mixing were measured through temperature and torque measuring sensors located between the two screws of the internal mixer reactor, and the graph of these measurements is shown in Figure 3. The measurement results confirmed that starch gelatinization was completed within 3 minutes from the start of mixing, and that the torque and temperature inside the reactor were maintained at 8 to 10 Nm and 96.9 ± 1°C, respectively, after starch gelatinization.

[0121] Subsequently, an additional purification step was performed in the same manner as in Example 1-1 to obtain purified carboxymethylated starch.

[0122] Reference Example 1-2 In an internal mixer reactor, 28 g of potato starch (manufactured by DAESANG, moisture content 17% by weight) (actual starch content considering moisture content: 23.24 g, 0.143 mol), 6.91 g of NaOH (0.173 mol, 1.2 equivalents relative to the number of starch moles), 20.11 g of SMCA (0.173 mol, 1.2 equivalents relative to the number of starch moles), 6 g of distilled water, and 6 g of glycerol were packed to 93% of the reactor volume, and the mixture was mixed at 50 rpm for 10 minutes to carry out the gelatinization and carboxymethylation reactions of starch.

[0123] At this time, the internal torque and temperature inside the reactor during mixing were measured through temperature and torque measuring sensors located between the two screws of the internal mixer reactor, and the graph of these measurements is shown in Figure 4. The measurement results confirmed that starch gelatinization was completed within 4 minutes from the start of mixing, and that the torque and temperature inside the reactor were maintained at 16 to 18 Nm and 102.5 ± 1°C, respectively, after starch gelatinization.

[0124] Subsequently, an additional purification step was performed in the same manner as in Example 1-1 to obtain purified carboxymethylated starch.

[0125] Reference Examples 1-3 In an internal mixer reactor, 28 g of potato starch (manufactured by DAESANG, moisture content 17% by weight) (actual starch content considering moisture content: 23.24 g, 0.143 mol), 6.91 g of NaOH (0.173 mol, 1.2 equivalents relative to the number of starch moles), 20.11 g of SMCA (0.173 mol, 1.2 equivalents relative to the number of starch moles), 6 g of distilled water, and 6 g of IPA were packed to 88% of the reactor volume, and the mixture was mixed at 50 rpm for 10 minutes to carry out the gelatinization and carboxymethylation reactions of starch.

[0126] At this time, the internal torque and temperature inside the reactor during mixing were measured through temperature and torque measuring sensors located between the two screws of the internal mixer reactor, and the graph of these measurements is shown in Figure 5. The measurement results confirmed that starch gelatinization was completed within 4 minutes from the start of mixing, and that the torque and temperature inside the reactor were maintained at 12 to 15 Nm and 98.4 ± 1°C, respectively, after starch gelatinization.

[0127] Subsequently, an additional purification step was performed in the same manner as in Example 1-1 to obtain purified carboxymethylated starch.

[0128] The starch content, water content, total water content, amount of water and additional solvent used relative to the weight of starch, and equivalent amounts of NaOH and SMCA used in the aforementioned examples, comparative examples, and reference examples are summarized in Table 1 below.

[0129] Examples - Production of superabsorbent polymers Example 2-1 (Step 1) The carboxymethylated starch produced in Example 1-1 was dissolved in water at a weight 10 times the weight of the carboxymethylated starch.

[0130] (Step 2) Subsequently, the product from step 1, which has a pH of 7.5 to 8, was adjusted to pH 6.5 using a 3% hydrochloric acid aqueous solution. Under this pH, a crosslinked polymer was produced by drying and self-crosslinking reaction for 2 to 3 hours in an oven with adjustable airflow direction, supplying 120°C hot air.

[0131] (Additional steps) Subsequently, the cross-linked polymer was pulverized using a pulverizer, then classified to separate particles with a size of 150 to 850 μm, which were then used as the final product, a superabsorbent polymer.

[0132] Example 2-2, Comparative Example 2-1, Comparative Example 2-2, and Reference Examples 2-1 to 2-3 A superabsorbent polymer was produced using the same method as in Example 2-1, except that the carboxymethylated starch produced in Example 1-2, Comparative Example 1-1, Comparative Example 1-2, and Reference Examples 1-1 to 1-3 were used instead of the carboxymethylated starch produced in Example 1-1.

[0133] Test Example 1: Measurement of the degree of substitution of carboxymethylated starch (1) Measurement of the actual degree of substitution First, each of the carboxymethylated starches produced in the above examples, comparative examples, and reference examples 1 Prepare the sample for 1H NMR analysis. 1 We obtained an 1H NMR spectrum. Specifically, 1 For 1H NMR analysis, carboxymethylated starch dissolved in H2O was added to MeOH and stirred. After filtration, the mixture was dried to prepare 50 mg of the sample. The prepared sample was then dissolved in 0.75 mL of D2O and 0.25 mL of D2SO4, which are the NMR measurement solvents, and stirred at 90°C for 1 hour. The sample was then observed to have turned a deep yellow color.

[0134] Subsequently, Figures 6 to 10 show the carboxymethylated starch produced in Example 1-1, Example 1-2, Reference Example 1-1, Reference Example 1-2, and Reference Example 1-3, respectively. 1 The 1H NMR spectrum is shown.

[0135] More specifically, the degree of substitution of the carboxymethylated starch produced in Example 1-1 was measured as follows.

[0136] 1) Carboxymethylated starch produced in Example 1-1 1 After obtaining the 1H NMR spectrum, the settings were adjusted so that the sum of the integrals of the peaks within the 2.5-3.6 ppm range—2.57 ppm, 2.58 ppm, 2.60 ppm, 2.64 ppm, 2.66 ppm, 3.15 ppm, 3.16 ppm, 3.33 ppm, and 3.34 ppm—was 1.

[0137] 2) Next, the degree of substitution at the second carbon (2-DS) was determined as the sum of the integral values ​​at the peaks of 3.34 ppm, 3.33 ppm (doublet, 0.23), and 2.57 ppm, 2.58 ppm (doublet, 0.20). The degree of substitution at the third carbon (3-DS) was determined by dividing the integral values ​​at the peaks of 2.39 ppm and 2.41 ppm (0.20) by 2. The degree of substitution at the sixth carbon (6-DS) was determined by dividing the integral values ​​at the peaks of 2.14 ppm and 2.15 ppm (0.19) by 2.

[0138] 3) Then, the degree of substitution at the second carbon (2-DS), the degree of substitution at the third carbon (3-DS), and the degree of substitution at the sixth carbon (6-DS) were all added together to determine the degree of substitution (DS) of the carboxylmethyl group.

[0139] By a similar method, the degree of substitution of carboxymethyl groups in carboxymethylated starch prepared in other examples, comparative examples, and reference examples was determined, and substantially 1Since some degree of shift in the 1H NMR spectrum is possible, the measurement results of the degree of substitution are shown in Table 2, compared with the spectrum of Example 1-1.

[0140] (2) Calculation of reaction efficiency (RE, %) The reaction efficiency (RE, %) was calculated using the formula 1 below, and the results are shown in Table 2. [Formula 1] Reaction efficiency (RE, %) = [(Actual degree of substitution) / (Expected degree of substitution)] × 100 In the above formula 1, The expected degree of substitution refers to the equivalent amount of SMCA added relative to the number of moles of starch.

[0141] Test Example 2: Measurement of Centrifuge Retention Capacity (CRC) of Superabsorbent Polymers The water retention capacity of the superabsorbent polymers produced in the examples, comparative examples, and reference examples was measured according to the European Disposables and Nonwovens Association (EDANA) standard EDANA WSP 241.3, and the results are shown in Table 3.

[0142] Specifically, the superabsorbent polymers produced in the examples, comparative examples, and reference examples were classified using a #30-50 sieve to obtain only superabsorbent polymers having a particle size of 300 to 600 μm. Such superabsorbent polymers W0 (g) (approximately 0.17 g) were uniformly placed in a nonwoven fabric envelope and sealed, and then immersed in physiological saline (0.9 wt%) at room temperature. After 30 minutes, the envelope was drained for 3 minutes under conditions of 250 G using a centrifuge, and the mass of the envelope W2 (g) was measured.

[0143] Furthermore, the same procedure was performed without using resin, and the mass W1 (g) at that time was measured. Using the obtained masses, the CRC (g / g) was calculated using the following formula 2. [Formula 2] CRC(g / g)={[W2(g)-W1(g)] / W0(g)}-1

[0144] [Table 1]

[0145] [Table 2]

[0146] [Table 3]

[0147] Referring to Tables 1 to 3 above, it can be seen that in the example manufacturing method in which the starch gelatinization and carboxymethylation reaction is carried out using a specific amount of water, and a specific level of torque is maintained after the starch gelatinization, the reaction efficiency is significantly improved compared to the manufacturing method of Comparative Example 1-1, in which the starch gelatinization and carboxymethylation reaction is carried out using an excess amount of solvent according to a commonly known manufacturing method.

[0148] Furthermore, in the case of carboxymethylated starch produced in Comparative Examples 1-2, although a similar amount of SMCA was used and the degree of substitution was similar to that of the Examples, the water retention capacity of the final superabsorbent polymer produced was significantly lower than that of the superabsorbent polymer produced using the carboxymethylated starch of the Examples. This is judged to be because, unlike the Examples, sufficient torque was not induced in the flask reactor, and the torque could not be maintained at a constant level after the gelatinization of the starch, resulting in the inability to uniformly substitute carboxymethyl groups into the carboxymethylated starch of the Examples.

[0149] Furthermore, Comparative Examples 1-3 confirmed that when the water content is excessively low during the gelatinization and carboxymethylation reactions of starch, the internal torque of the reactor continues to increase after gelatinization, making it impossible to produce uniformly substituted carboxymethylated starch.

[0150] Furthermore, as can be seen from Reference Examples 1-1 to 1-3, by adjusting the equivalent amounts of the reactants to the appropriate amounts and using water as the sole solvent for carboxymethylation, the efficiency of the carboxymethylation reaction can be further improved.

Claims

1. The process includes the step of mixing polysaccharides, hydroxides, metal salts of haloalkylcarboxylic acids and water in an internal mixer to carry out the gelatinization and carboxyalkylation reactions of the polysaccharides. The water used is in an amount equal to 0.45 to 0.75 times the weight of the polysaccharide. After the gelatinization of the polysaccharide, the torque in the internal mixer is maintained at 7 to 18 Nm. No solvents other than water are used. The hydroxide is used in an equivalent amount of 0.5 or more and less than 1.2 relative to the number of moles obtained by dividing the weight (g) of the polysaccharide by the molecular weight of anhydrous glucose units (AGU). The aforementioned polysaccharide is starch, The carboxyalkylated polysaccharide is carboxymethylated, The metal salt of the aforementioned haloalkylcarboxylic acid is an alkali metal salt of chloroacetate. A method for producing carboxyalkylated polysaccharides.

2. The manufacturing method according to claim 1, wherein the water is used in an amount equal to 0.6 to 0.75 times the weight of the polysaccharide.

3. The manufacturing method according to claim 1, wherein the degree of substitution (DS) of the carboxyalkyl group in the carboxyalkylated polysaccharide produced is 0.6 to 1.

1.

4. The manufacturing method according to claim 1, wherein the mixing is performed when the internal mixer is filled to 70 to 95% of its total volume.

5. The manufacturing method according to claim 1, wherein the hydroxide is one or more selected from the group consisting of sodium hydroxide, potassium hydroxide, and lithium hydroxide.

6. The manufacturing method according to claim 1, wherein the hydroxide is used in an equivalent amount of 0.6 to 0.8 with respect to the number of moles obtained by dividing the weight (g) of the polysaccharide by the molecular weight of anhydrous glucose units (AGU).

7. The manufacturing method according to claim 1, wherein the alkali metal chloroacetate salt is one or more selected from the group consisting of sodium monochloroacetate (SMCA), potassium monochloroacetate, and lithium monochloroacetate.

8. The manufacturing method according to claim 1, wherein the metal salt of the haloalkylcarboxylic acid is used in an amount of 1 to 1.29 moles per mole of the hydroxide.

9. The manufacturing method according to claim 1, wherein the mixing is carried out for 5 to 15 minutes.

10. The manufacturing method according to claim 1, wherein the gelatinization of the polysaccharide is completed within 2 / 5 of the total mixing time from the start of mixing.

11. The manufacturing method according to claim 1, wherein the temperature inside the internal mixer is maintained at 90 to 110°C after the gelatinization of the polysaccharide.

12. The manufacturing method according to claim 1, further comprising the step of dissolving the manufactured product in water and then precipitating it in an alcohol-based organic solvent.

13. The method for producing an alcoholic organic solvent according to claim 12, wherein the alcoholic organic solvent is one or more selected from the group consisting of methanol, ethanol, and isopropyl alcohol.

14. Step 1: Dissolve a carboxyalkylated polysaccharide produced by any one of claims 1 to 13 in water in an amount of 5 to 15 times the weight of the carboxyalkylated polysaccharide; Step 2 includes a step of self-crosslinking the product from step 1 while drying it under pH 6 to 8 conditions. A method for producing biodegradable superabsorbent polymers.

15. The manufacturing method according to claim 14, wherein the superabsorbent polymer produced satisfies the centrifugal separation water retention capacity (CRC) of the superabsorbent polymer measured by the EDANA method WSP 241.3, which is 30 to 45 g / g.

16. The manufacturing method according to claim 14, wherein the dissolution in step 1 is carried out under room temperature and atmospheric pressure conditions.

17. The manufacturing method according to claim 14, wherein the drying in step 2 is carried out at a temperature of 100 to 130°C.

18. The manufacturing method according to claim 14, further comprising the steps of grinding and classifying the crosslinked polymer produced in step 2, from step 2 onward.

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