Method for Manufacturing Eco-Friendly Cellulose-Based Superabsorbent Hydrogel Using Electron Beam Crosslinking and Eco-Friendly Cellulose-Based Superabsorbent Hydrogel Manufactured by the same

Abstract

The present invention relates to a method for manufacturing an eco-friendly cellulose-based superabsorbent hydrogel, and more specifically, to a method for manufacturing a hydrogel with excellent biocompatibility and water absorption capacity through a simple crosslinking process while effectively mixing a high concentration of cellulose derivative solutions.

Description

Technology Field

[0001] The present invention relates to a method for manufacturing an eco-friendly cellulose-based superabsorbent hydrogel using electron beam crosslinking and an eco-friendly cellulose-based superabsorbent hydrogel manufactured thereby. Background Technology

[0003] Hydrogels with a three-dimensional cross-linked network structure are superabsorbent materials capable of absorbing large amounts of water. They do not dissolve easily in water and can maintain a swollen state without releasing moisture even under external pressure after absorbing it, so they are widely used in various fields such as medical patches, disposable hygiene products, agricultural moisture regulators, and cosmetics.

[0004] Hydrogels can be classified into petroleum-based polymers and natural polymers depending on the feedstock. Petroleum-based hydrogels are primarily manufactured based on synthetic polymers such as polyacrylates and polyacrylamides. They are widely used commercially because they are easy to mass-produce, inexpensive, and possess excellent physical properties such as high water absorption and superior physical strength. However, regulations on petroleum-based superabsorbent polymers are being tightened due to issues such as biotoxicity, non-biodegradability, and the depletion of petroleum resources.

[0005] Accordingly, research on eco-friendly hydrogels based on natural polymers has recently been actively conducted, and hydrophilic polymers such as chitosan, alginate, and cellulose are mainly used in the manufacture of eco-friendly absorbent materials. These natural polymers are attracting attention as alternatives to petroleum-based polymers because they are sustainable materials obtained from nature, are biodegradable, and are non-toxic. In particular, cellulose-based derivatives such as CMC (Carboxymethyl cellulose), in which hydroxyl groups on the surface of cellulose are modified into carboxyl groups, are highly suitable materials for hydrogel manufacturing because they are hydrophilic enough to dissolve easily in water.

[0006] Hydrogels based on cellulose derivatives can generally be prepared through physical, chemical, and radiation crosslinking. Physical crosslinking forms crosslinked structures through intermolecular or intramolecular hydrogen bonds, electrostatic interactions, and other non-covalent bonds; it does not require chemical additives and offers excellent biocompatibility. However, it has the disadvantage that the crosslinked structure can easily collapse due to changes in the external environment, such as pH and temperature. On the other hand, chemical crosslinking uses crosslinking agents to form covalent bonds between polymer chains, enabling the creation of structures with relatively high strength and stability. While crosslinking agents such as epichlorohydrin (ECH) and glutaraldehyde (GA) are primarily used for chemical crosslinking, these are classified as toxic chemicals, and residual chemicals may remain within the hydrogel after crosslinking, potentially causing toxicity issues. Radiation crosslinking is a method of inducing crosslinking using high-energy radiation such as alpha rays, gamma rays, X-rays, and electron beams. When cellulose is irradiated with radiation, polymer chains are cleaved to generate free radicals, and these highly reactive free radicals can form new covalent bonds with surrounding radicals or molecular chains. As such, the radiation crosslinking method allows for the production of hydrogels without chemical crosslinking agents or catalysts. It also has excellent biocompatibility, eco-friendliness, and processing efficiency because it eliminates the problem of residual toxic substances and does not require additional washing processes.

[0007] When preparing hydrogels by electron beam irradiation, the degree of substitution (DS) and concentration of the cellulose derivative significantly affect the crosslinking efficiency. When the degree of substitution of the cellulose derivative is 1.5 or higher, crosslinks can be effectively formed even in an aqueous solution with a concentration of approximately 5 wt%. However, when the degree of substitution of the cellulose derivative is less than 1.5, the intermolecular reactivity is low, making it difficult to form crosslinks at low concentrations of less than 5 wt%. Specifically, in aqueous solutions with a low concentration of less than 5 wt%, water molecules can increase the distance between cellulose molecules, thereby inhibiting the formation of crosslinks. At the same time, the problem of glycosidic bonds within cellulose molecules being easily decomposed by the electron beam may occur. On the other hand, at concentrations of 5 wt% or higher, viscosity increases significantly, making homogeneous mixing difficult. Thus, when the degree of substitution is low, a higher concentration of the cellulose derivative aqueous solution is required, which can make the mixing and processing difficult.

[0008] Accordingly, there is a need for a technology capable of producing non-toxic, eco-friendly superabsorbent materials that are biodegradable for the protection of the environment and the human body, while having physical properties such as water absorption equivalent to existing fossil fuel-derived superabsorbent polymer (SAP) materials. Specifically, there is a need for a technology capable of effectively mixing high-concentration cellulose derivative solutions and producing hydrogels with excellent biocompatibility and water absorption through a simple cross-linking process. The problem to be solved

[0010] The problem that the present invention aims to solve is to provide a method for producing an eco-friendly cellulose-based superabsorbent hydrogel with excellent biocompatibility and water absorption capacity using electron beam crosslinking while effectively mixing high concentrations of cellulose derivatives, and to provide the eco-friendly cellulose-based superabsorbent hydrogel produced by this method.

[0011] However, the problems that the present invention aims to solve are not limited to those mentioned above, and other unmentioned problems will be clearly understood by those skilled in the art from the description below. means of solving the problem

[0013] One embodiment of the present invention provides a method for manufacturing an eco-friendly cellulose-based superabsorbent hydrogel comprising: a step of preparing a cellulose suspension comprising a cellulose raw material including a cellulose-based derivative, an organic acid-based crosslinking agent, and a solvent; a step of preparing a cellulose pre-gel by stirring the cellulose suspension; and a step of preparing a hydrogel by irradiating the cellulose pre-gel with radiation, wherein the temperature of the solvent is 40°C or higher.

[0014] In addition, one embodiment of the present invention provides an eco-friendly cellulose-based superabsorbent hydrogel produced by the above manufacturing method. Effects of the invention

[0016] A method for manufacturing an eco-friendly cellulose-based superabsorbent hydrogel according to one embodiment of the present invention can effectively mix a high-viscosity cellulose derivative and a solvent.

[0017] In addition, the method for manufacturing a cellulose-based hydrogel according to one embodiment of the present invention can manufacture the hydrogel within a short processing time through radiation crosslinking, and may not require a chemical crosslinking agent and an additional washing process.

[0018] In addition, the eco-friendly cellulose-based superabsorbent hydrogel according to one embodiment of the present invention may have superior biocompatibility and biodegradability compared to conventional petrochemical superabsorbent polymers (SAP).

[0019] In addition, the eco-friendly cellulose-based superabsorbent hydrogel according to one embodiment of the present invention is biodegradable and eco-friendly, and can have excellent physical properties such as initial water absorption rate and water absorption amount.

[0020] The effects of the present invention are not limited to those described above, and unmentioned effects will be clearly understood by those skilled in the art from the present specification and the accompanying drawings. Brief explanation of the drawing

[0022] Figure 1 is an SEM cross-sectional image of a hydrogel according to Examples 1-3, Comparative Examples 1-1 and 2-1. Specific details for implementing the invention

[0023] When a part of the entire specification is described as "comprising" a certain component, this means that, unless specifically stated otherwise, it does not exclude other components but may include additional components.

[0024] Throughout this specification, the term “viscosity” means a value measured using a Brookfield viscometer in accordance with the international standard ASTM / ISO 2555.

[0025] In describing the principles of a preferred embodiment of the present invention in detail, if it is determined that a specific description of related known functions or configurations could unnecessarily obscure the essence of the present invention, such detailed description is omitted.

[0027] One embodiment of the present invention provides a method for manufacturing an eco-friendly cellulose-based superabsorbent hydrogel comprising: a step of preparing a cellulose suspension comprising a cellulose raw material including a cellulose-based derivative, an organic acid-based crosslinking agent, and a solvent; a step of preparing a cellulose pre-gel by stirring the cellulose suspension; and a step of preparing a hydrogel by irradiating the cellulose pre-gel with radiation, wherein the temperature of the solvent is 40°C or higher.

[0028] A method for manufacturing a hydrogel according to one embodiment of the present invention will be described in more detail step by step below.

[0029] According to one embodiment of the present invention, a cellulose suspension is first prepared comprising a cellulose raw material containing a cellulose-based derivative, an organic acid-based crosslinking agent, and a solvent. The cellulose suspension can be prepared by mixing the cellulose raw material, the organic acid-based crosslinking agent, and the solvent.

[0031] According to one embodiment of the present invention, the cellulose raw material comprises a cellulose-based derivative. Specifically, the cellulose raw material may comprise a biomass-based cellulose-based derivative. When a cellulose suspension is prepared using the cellulose raw material, the resulting hydrogel may have excellent biodegradability, be environmentally friendly, and have excellent water absorption.

[0032] According to one embodiment of the present invention, the cellulose-based derivative may comprise at least one of hydroxycellulose, hydroxyethyl cellulose (HEC), hydroxypropyl methyl cellulose (HPMC), hydroxypropyl cellulose (HPC), hydroxybutyl methyl cellulose (HBMC), carboxycellulose, carboxymethyl cellulose (CMC), carboxyethyl cellulose (CECMC), sulfated cellulose (SC), sulfated carboxymethyl cellulose (S-CMC), and phosphorylated cellulose (PC). Preferably, the cellulose-based derivative may include carboxymethyl cellulose. The cellulose-based derivative may be one in which hydroxyl groups present in the repeating units of cellulose are substituted by etherification, carboxymethylation, sulfation, or phosphorylation reactions. When the cellulose raw material includes the aforementioned cellulose-based derivative, physical properties such as the initial water absorption rate and water absorption amount of the hydrogel being manufactured can be effectively improved.

[0034] According to one embodiment of the present invention, the viscosity of the cellulose-based derivative may be 1,000 cPs or more and 10,000 cPs or less, as measured according to the international standard ASTM / ISO 2555. Specifically, it may be 1,000 cPs or more and 5,000 cPs or less. When the viscosity of the cellulose-based derivative is within the aforementioned range, the strength of the network structure may be increased by increasing the crosslinking density of the hydrogel being manufactured. Accordingly, the water absorption capacity may be improved, and a hydrogel with high biocompatibility can be manufactured.

[0036] According to one embodiment of the present invention, the content of the cellulose-based derivative may be 5 parts by weight or more and 15 parts by weight or less with respect to 100 parts by weight of the cellulose suspension. Specifically, it may be 7 parts by weight or more and 15 parts by weight or less, 9 parts by weight or more and 15 parts by weight or less, 5 parts by weight or more and 13 parts by weight or less, 7 parts by weight or more and 13 parts by weight or less, 9 parts by weight or more and 13 parts by weight or less, 5 parts by weight or more and 11 parts by weight or less, 7 parts by weight or more and 11 parts by weight or less, or 9 parts by weight or more and 11 parts by weight or less. By controlling the content of the cellulose-based derivative contained in the suspension to the aforementioned range, the eco-friendly cellulose-based superabsorbent hydrogel can be effectively manufactured, and physical properties such as the initial water absorption rate and water absorption amount of the manufactured eco-friendly cellulose-based superabsorbent hydrogel can be effectively improved.

[0038] According to one embodiment of the present invention, the organic acid-based crosslinking agent may comprise a carboxylic acid compound. More specifically, the carboxylic acid compound may comprise at least one carboxyl group in its molecular structure. Specifically, the carboxylic acid-based compound may comprise at least one of lactic acid, acetic acid, propionic acid, glycolic acid, citric acid, malic acid, tartaric acid, oxalic acid, gluconic acid, succinic acid, fumaric acid, adipic acid, ethylenediaminetetraacetic acid (EDTA), and polyglutamic acid. Preferably, the organic acid-based crosslinking agent may be citric acid.

[0039] According to one embodiment of the present invention, by using an organic acid-based crosslinking agent comprising a carboxylic acid-based compound, crosslinking between the reactive groups of the cellulose-based derivative can be effectively formed. Specifically, the organic acid-based crosslinking agent controls the reaction pathway of free radicals generated by radiation to promote the formation of a three-dimensional network, thereby enabling the formation of a hydrogel with enhanced strength and network structure. Additionally, the water absorption performance of the manufactured cellulose-based hydrogel can be improved.

[0040] According to one embodiment of the present invention, the content of the organic acid-based crosslinking agent may be greater than 0 parts by weight and less than or equal to 10 parts by weight per 100 parts by weight of the cellulose suspension. Specifically, it may be greater than 0 parts by weight and less than or equal to 7 parts by weight, or greater than 0 parts by weight and less than or equal to 5 parts by weight. When the content of the organic acid-based crosslinking agent is within the aforementioned range, physical properties such as the initial water absorption rate and water absorption amount of the eco-friendly cellulose-based superabsorbent hydrogel produced can be effectively improved. Furthermore, by effectively promoting the crosslinking reaction caused by radiation, a hydrogel with excellent strength and network stability can be produced.

[0042] According to one embodiment of the present invention, distilled water, water, acetone, ethanol, methanol, etc., may be used as the solvent. When the solvent is used, the dissolution or dispersion of the cellulose-based derivative can be promoted to form a uniform mixture, and accordingly, a cellulose-based superabsorbent hydrogel can be effectively manufactured.

[0043] According to one embodiment of the present invention, the temperature of the solvent is 40°C or higher. Specifically, it may be 45°C or higher and 100°C or lower, 50°C or higher and 100°C or lower, 55°C or higher and 100°C or lower, or 60°C or higher and 100°C or lower. By using a solvent with a temperature satisfying the aforementioned ranges, the manufacturing efficiency of the cellulose-based hydrogel can be improved and the process time can be shortened. Specifically, a high-viscosity cellulose-based derivative and a solvent can be effectively mixed to produce a high-viscosity and high-concentration cellulose suspension, and accordingly, the uniformity and strength of the network structure during hydrogel formation can be improved, thereby improving the physical properties of the hydrogel. Furthermore, by using a cellulose suspension containing a high-viscosity cellulose-based derivative, the amount of water absorbed can be improved.

[0044] According to one embodiment of the present invention, the cellulose derivative can be obtained by substituting cellulose present in the cellulose raw material. Specifically, it can be obtained by substituting the hydroxyl groups present in the cellulose through etherification, carboxymethylation, sulfation, or phosphorylation reactions. Preferably, the cellulose derivative is obtained by substituting the hydroxyl groups (-OH) of the cellulose with carboxymethyl groups (-CH2COO) through a carboxymethylation reaction. - It may be formed by substituting with ). Specifically, it may be formed by adding an alkali agent, a carboxymethylating agent, and an organic solvent or an aqueous solution of an organic solvent to a raw material containing cellulose to form a mixed solution, and then causing a carboxymethylation reaction to form carboxymethyl cellulose (CMC). In the step of substituting the cellulose, the hydroxyl groups present in the cellulose may be substituted by a substitution reaction, and the degree of substitution (DS) of the carboxymethyl cellulose produced may be controlled by adjusting the content of the alkali agent, carboxymethylating agent, and organic solvent, as well as the reaction temperature and reaction time. For example, if all three hydroxyl groups present in the cellulose are substituted, the degree of substitution may have a maximum value of 3, and if only one hydroxyl group is substituted, the degree of substitution may have a value of 1.

[0045] According to one embodiment of the present invention, the degree of substitution of the cellulose-based derivative included in the cellulose raw material may be 0.1 to 3.0. Specifically, the degree of substitution of the cellulose-based derivative may be 0.5 to 3.0, 0.5 to 2.5, 0.5 to 2.0, 0.5 to 1.5, 0.6 to 1.0, 0.6 to 0.9, or 0.7 to 1.0. When using a cellulose-based derivative satisfying the degree of substitution within the aforementioned range, physical properties such as the initial water absorption rate and water absorption amount of the hydrogel being manufactured can be effectively improved.

[0047] According to one embodiment of the present invention, a cellulose pre-gel is prepared by stirring the cellulose suspension.

[0048] According to one embodiment of the present invention, the cellulose pregel may be in a physical gel state. Specifically, by performing the stirring, hydrogen bonding may occur between the hydroxyl group (-OH) of the cellulose derivative and the carboxyl group (-COOH) of the organic acid crosslinking agent, and a physical network structure may be formed due to the occurrence of the hydrogen bonding. As the physical network structure is formed, the cellulose suspension may become a pregel in a physical gel state. The cellulose pregel may be in a state where gelation proceeds as a physical network is formed while physical interactions, such as hydrogen bonding and electrostatic attraction between the cellulose derivatives, increase, and may have increased viscosity and fluidity.

[0049] According to one embodiment of the present invention, the stirring may be performed using a vacuum stirring degassing machine.

[0050] According to one embodiment of the present invention, the stirring may be performed at a speed of 50 rpm to 1000 rpm. Specifically, it may be performed at a speed of 100 rpm to 800 rpm, 200 rpm to 600 rpm, or 300 rpm to 500 rpm.

[0051] According to one embodiment of the present invention, the stirring may be performed at a temperature of 20°C or higher and 100°C or lower. Specifically, it may be performed at a temperature of 20°C or higher and 90°C or lower, 20°C or higher and 80°C or lower, 20°C or higher and 70°C or lower, 20°C or higher and 60°C or lower, 20°C or higher and 50°C or lower, or 20°C or higher and 40°C or lower.

[0052] According to one embodiment of the present invention, the stirring may be performed under a pressure of 0.2 bar to 2.0 bar. Specifically, it may be performed under a pressure of 0.2 bar to 1.8 bar, 0.2 bar to 1.6 bar, 0.2 bar to 1.4 bar, 0.2 bar to 1.1 bar, 0.2 bar to 1.0 bar, 0.3 bar to 1.0 bar, 0.4 bar to 1.0 bar, 0.5 bar to 1.0 bar, 0.6 bar to 1.0 bar, 0.7 bar to 1.0 bar, or 0.7 bar to 0.9 bar.

[0053] According to one embodiment of the present invention, the stirring may be performed for more than 0 minutes and less than or equal to 300 minutes. Specifically, it may be performed for 5 minutes or more and less than or equal to 300 minutes, 5 minutes or more and less than or equal to 270 minutes, 5 minutes or more and less than or equal to 240 minutes, 5 minutes or more and less than or equal to 210 minutes, 5 minutes or more and less than or equal to 180 minutes, 5 minutes or more and less than or equal to 150 minutes, 10 minutes or more and less than or equal to 100 minutes.

[0054] According to one embodiment of the present invention, by performing stirring within the aforementioned ranges of stirring speed, temperature, and time, the cellulose-based derivative and the crosslinking agent can be uniformly mixed even as the viscosity of the solution gradually increases, and the formation of bubbles in the finally prepared hydrogel can be effectively reduced. A hydrogel with fewer bubbles can form a smoother and more uniform surface, thereby increasing biocompatibility, and can improve water absorption and retention capacity by evenly absorbing and retaining water through the network structure within the hydrogel. Furthermore, the reduction of bubbles can improve the strength and stability of the hydrogel, thereby improving the overall physical properties of the hydrogel.

[0056] According to one embodiment of the present invention, a hydrogel is formed by irradiating the cellulose pregel with radiation. Specifically, by irradiating with radiation, the cellulose pregel can be made to form a hydrogel by forming a three-dimensional network structure. More specifically, by irradiating the cellulose pregel with radiation, free radicals can be generated within the molecules of the cellulose derivative, and the free radicals can be made to combine with each other to form a three-dimensional network structure. Accordingly, the cellulose pregel can be converted into a hydrogel.

[0057] According to one embodiment of the present invention, the radiation may be gamma rays, electron beams, ion beams, or neutron rays.

[0058] According to one embodiment of the present invention, when the radiation is a gamma ray, an electron beam, an ion beam, or a neutron beam, the dose of the radiation may be 30 kGy or less. Specifically, the dose of the radiation may be 5 kGy or more and 20 kGy or less, 5 kGy or more and 15 kGy or less, 5 kGy or more and 10 kGy or less, 5 kGy or more and 7 kGy or less, 6 kGy or more and 30 kGy or less, 6 kGy or more and 20 kGy or less, 6 kGy or more and 15 kGy or less, 6 kGy or more and 10 kGy or less, or 6 kGy or more and 7 kGy or less. By irradiating the cellulose pregel with radiation within the dose range described above, a hydrogel with excellent physical properties can be formed. Specifically, the glycosidic bond decomposition reaction within the cellulose derivative molecules of the cellulose pregel can be minimized and cross-linking promoted to effectively form a three-dimensional network structure.

[0060] According to one embodiment of the present invention, the time for irradiating with radiation may be greater than 0 seconds and less than or equal to 300 seconds, greater than 0 seconds and less than or equal to 250 seconds, greater than 0 seconds and less than or equal to 200 seconds, greater than 0 seconds and less than or equal to 150 seconds, greater than 0 seconds and less than or equal to 100 seconds, greater than 0 seconds and less than or equal to 50 seconds, or greater than 0 seconds and less than or equal to 10 seconds. By controlling the time for manufacturing the hydrogel to the aforementioned range, a hydrogel with stable physical properties can be manufactured.

[0061] In addition, one embodiment of the present invention provides an eco-friendly cellulose-based superabsorbent hydrogel produced by the above manufacturing method.

[0062] A hydrogel according to one embodiment of the present invention may have excellent water absorption performance and gel fraction.

[0063] According to one embodiment of the present invention, the water absorption capacity (WAC) is defined as the mass (g) of water absorbed by 1 g of a dry hydrogel using the following [Equation 1].

[0064]

[0066] In the above Equation 1, W t is the amount of water absorbed (g / g) after t minutes or t hours, and M t is the mass (g) of the hydrogel after immersion in water for t minutes or t hours, and M0 is the mass (g) of the initially dried hydrogel.

[0067] According to one embodiment of the present invention, the water absorption capacity of the eco-friendly cellulose-based superabsorbent hydrogel produced by the above manufacturing method may be 20 g / g or more and 300 g / g or less. Specifically, the water absorption capacity of the hydrogel may be 50 g / g or more and 300 g / g or less, 100 g / g or more and 300 g / g or less, 150 g / g or more and 300 g / g or less, 50 g / g or more and 250 g / g or less, 100 g / g or more and 250 g / g or less, 150 g / g or more and 250 g / g or less, 200 g / g or more and 250 g / g or less, or 230 g / g or more and 250 g / g or less. The hydrogel satisfying the water absorption capacity within the aforementioned ranges can be effectively applied to an absorbent article.

[0068] According to one embodiment of the present invention, the gel fraction (GF) of the eco-friendly cellulose-based superabsorbent hydrogel may be 70% or more and 100% or less. Specifically, the gel fraction of the eco-friendly cellulose-based superabsorbent hydrogel may be 75% or more and 100% or less, or 80% or more and 100% or less. By satisfying the gel fraction within the aforementioned range, the hydrogel may be strongly cross-linked, resulting in high mechanical strength and structural stability, and may not dissolve even when exposed to water for a long time. The hydrogel satisfying the gel fraction within the aforementioned range can be effectively applied to absorbent articles.

[0069] According to one embodiment of the present invention, the solid content (SC) of the eco-friendly cellulose-based superabsorbent hydrogel may be 3% or more and 20% or less. By satisfying the solid content within the aforementioned range, the mechanical strength is sufficient, resulting in excellent stability, while also providing excellent water absorption.

[0071] According to one embodiment of the present invention, the absorbent article may include at least one of sanitary products, soil moisture regulators, absorbent pads, ice packs, and hydro patches. Specifically, the absorbent article may include at least one of sanitary products such as infant and adult diapers and feminine sanitary pads, soil moisture regulators for agriculture or horticulture, absorbent pads for food packaging, ice packs, and medical hydro patches. The absorbent article of the above types may be environmentally friendly as it possesses excellent moisture absorption capacity by including the hydrogel and is biodegradable, thereby reducing environmental pollution caused during incineration and landfill processes.

[0073] According to one embodiment of the present invention, the method for manufacturing the hydrogel may further include the steps of dehydrating, drying, and grinding the manufactured hydrogel. By further including the dehydration and drying steps, moisture can be effectively removed from the hydrogel, thereby enabling it to have an excellent moisture absorption capacity. By further including the grinding step, a hydrogel in powder form can be obtained. By transforming the hydrogel into a powder form, the hydrogel can be applied in a wider variety of ways.

[0074] According to one embodiment of the present invention, the step of dehydrating the hydrogel may involve vacuum filtration, gravity filtration, compression filtration, or vacuum filtration of the prepared hydrogel. When the dehydration step is performed in such a manner, moisture contained in the hydrogel during the drying step can be effectively removed, thereby improving drying efficiency and further reducing the time and cost of drying the hydrogel.

[0075] According to one embodiment of the present invention, the step of drying the hydrogel may involve drying the dehydrated hydrogel by one or more methods selected from hot air drying, vacuum drying, microwave drying, and freeze-drying. For example, a drying step may be performed by further performing hot air drying on the dehydrated hydrogel after microwave drying. Preferably, the drying step may involve freeze-drying the dehydrated hydrogel. By drying the hydrogel by the above method, the finally produced cellulose-based hydrogel may have excellent initial water absorption and a high water absorption capacity. In addition, the drying time may be shortened compared to natural drying and low-temperature drying methods below 60°C, and efficient drying of the hydrogel at a low cost may be possible. In particular, the physical properties of the finally produced cellulose-based hydrogel may be excellent by performing freeze-drying.

[0076] According to one embodiment of the present invention, the step of drying the hydrogel can be performed at a temperature of 60°C or higher and 200°C or lower under atmospheric pressure (1±0.2 atm) for a period of 1 hour or more and 24 hours or less. That is, the hydrogel can be dried through hot air drying.

[0077] Specifically, the hot air drying may be performed at a temperature of 60°C or higher and 200°C or lower, 800°C or higher and 200°C or lower, 100°C or higher and 200°C or lower, or 105°C or higher and 200°C or lower. Additionally, the hot air drying may be performed for a period of time of 1 hour or higher and 24 hours or lower, 1 hour or higher and 10 hours or lower, 1 hour or higher and 6 hours or lower, 1 hour or higher and 3 hours or lower, or 3 hours or higher and 6 hours or lower. If the temperature and time range of the hot air drying is within the aforementioned ranges, heat-induced damage to the hydrogel can be prevented. Furthermore, by controlling the temperature and time at which the hot air drying is performed to the aforementioned ranges, moisture within the hydrogel can be removed quickly and effectively. Moreover, compared to low-temperature drying methods that require a long drying time, the hydrogel can be dried quickly and at a low cost.

[0078] According to one embodiment of the present invention, the step of drying the hydrogel can be performed at a pressure of 1 mTorr or more and 50 mTorr or less and a temperature of 60 ℃ or more and 200 ℃ or less for a period of 1 hour or more and 24 hours or less. That is, the hydrogel can be dried through high-temperature reduced-pressure drying.

[0079] According to one embodiment of the present invention, the pressure at which the vacuum drying is performed may be 1 mTorr or more and 50 mTorr or less, 5 mTorr or more and 45 mTorr or less, 10 mTorr or more and 40 mTorr or less, 15 mTorr or more and 35 mTorr or less, or 20 mTorr or more and 30 mTorr or less. By adjusting the pressure at which the vacuum drying is performed to the aforementioned range, moisture within the hydrogel can be removed quickly and effectively.

[0080] According to one embodiment of the present invention, when the hydrogel is subjected to high-temperature reduced-pressure drying, the temperature at which the reduced-pressure drying is performed may be 60°C or higher and 200°C or lower, 800°C or higher and 200°C or lower, 100°C or higher and 200°C or lower, or 105°C or higher and 200°C or lower. Additionally, the hot air drying may be performed for a period of time ranging from 1 hour to 24 hours or less, from 1 hour to 10 hours or less, from 1 hour to 6 hours or less, from 1 hour to 3 hours or less, or from 3 hours to 6 hours or less. If the temperature, pressure, and time ranges for the reduced-pressure drying are within the above ranges, heat-induced damage to the hydrogel can be prevented. By controlling the temperature, pressure, and time at which the reduced-pressure drying is performed to the aforementioned ranges, moisture within the hydrogel can be removed quickly and effectively. Furthermore, energy efficiency can be increased, and drying of the hydrogel can be achieved quickly and at a low cost. In addition, the dried hydrogel can have a moisture absorption capacity suitable for application to absorbent materials.

[0081] According to one embodiment of the present invention, the hydrogel produced by the dehydration and drying method described above may not undergo deformation of the cross-linking structure and may prevent deformation of the physical properties of the hydrogel, so that the gel fraction may not decrease even after dehydration and drying.

[0082] According to one embodiment of the present invention, the prepared hydrogel may further include a step of obtaining a hydrogel in powder form by grinding the dried hydrogel to a size of 0.1 mm to 50 mm in diameter after the dehydration and drying steps. Specifically, the grinding may involve grinding the dried hydrogel to a size of 0.1 mm to 30.0 mm, 0.1 mm to 10.0 mm, 0.1 mm to 5.0 mm, 10.0 mm to 50.0 mm, 10.0 mm to 30.0 mm, 20.0 mm to 50.0 mm, or 20.0 mm to 30.0 mm in diameter. When grinding is performed by controlling the particle size within the aforementioned ranges, the water absorption capacity and maximum water absorption capacity of the prepared hydrogel powder can be effectively improved. Furthermore, the grinding may be performed by a conventional method, such as grinding using a grinder. The hydrogel powder formed above can be applied in a wider variety of industrial fields.

[0084] The present invention will be described in more detail below with reference to preferred embodiments. However, it will be obvious to those skilled in the art that these embodiments are intended to explain the invention more specifically and that the scope of the invention is not limited by them.

[0086] Preparation of eco-friendly cellulose-based superabsorbent hydrogel

[0087] Example 1-1

[0088] A cellulose suspension was prepared by mixing carboxymethyl cellulose (Carboxymethyl Cellulose 1000 Cps, Zouping Yizhong Industrial Co., Ltd.), which has a degree of substitution of 0.8 as a cellulose raw material and a viscosity of 1,000 cPs measured using a Brookfield viscometer according to the international standard ASTM / ISO 2555, and citric acid (Citric acid anhydrous, DAEJUNG CHEMICALS & METALS Co., Ltd.) as a crosslinking agent with distilled water at 90°C. Based on 100 parts by weight of the cellulose suspension, the content of carboxymethyl cellulose was 9.8 parts by weight, and the content of citric acid was 2.4 parts by weight based on 100 parts by weight of the cellulose suspension.

[0089] Afterwards, the mixture was stirred using a vacuum stirring degassing machine at 25°C and 0.8 bar at 300 rpm until it became completely transparent when observed visually.

[0090] An eco-friendly cellulose-based superabsorbent hydrogel was prepared by irradiating the above cellulose pregel with a 7 kGy electron beam for 7 seconds.

[0092] Examples 1-2

[0093] An eco-friendly cellulose-based superabsorbent hydrogel was prepared in the same manner as in Example 1-1, except that carboxymethyl cellulose with a viscosity of 2,000 cPs (Carboxymethyl Cellulose 2000 Cps, Zouping Yizhong Industrial Co., Ltd.) was used.

[0095] Examples 1-3

[0096] An eco-friendly cellulose-based superabsorbent hydrogel was prepared in the same manner as in Example 1-1, except that carboxymethyl cellulose with a viscosity of 3,000 cPs (Carboxymethyl Cellulose 3000 Cps, Zouping Yizhong Industrial Co., Ltd.) was used.

[0098] Examples 1-4

[0099] An eco-friendly cellulose-based superabsorbent hydrogel was prepared in the same manner as in Example 1-1, except that carboxymethyl cellulose with a viscosity of 5,000 cPs (Carboxymethyl Cellulose 5000 Cps, Zouping Yizhong Industrial Co., Ltd.) was used.

[0101] Example 2-1

[0102] An eco-friendly cellulose-based superabsorbent hydrogel was prepared in the same manner as in Examples 1-3, except that the content of added carboxymethyl cellulose was 9.0 parts by weight based on 100 parts by weight of the cellulose suspension and the content of citric acid was 0.4 parts by weight based on 100 parts by weight of the cellulose suspension.

[0104] Comparative Example 1-1

[0105] An eco-friendly cellulose-based superabsorbent hydrogel was prepared using the same method as in Example 1-1, except that the temperature of the distilled water used in Example 1-1 was 25 ℃.

[0107] Comparative Example 2-1

[0108] An eco-friendly cellulose-based superabsorbent hydrogel was prepared using the same method as in Example 1-1, except that a vacuum stirring degassing machine was not used in Example 1-1.

[0110] Experimental Example 1. Evaluation of Stirring Time

[0111] In Examples 1-1 to 2-1 and Comparative Examples 1-1 to 2-1, the time taken for the solution to become completely transparent when mixed and observed visually during stirring is shown in Table 1 below.

[0113] Stirring time (h) Example 1-1 0.25 Examples 1-2 0.5 Examples 1-3 1 Examples 1-4 1.5 Example 2-1 1 Comparative Example 1-1 16 Comparative Example 2-1 1.5

[0115] Referring to Table 1 above, it was confirmed that the stirring time of Examples 1-1 to 1-4 and Example 2-1, which used distilled water of 60°C or higher as a solvent, was 1.5 hours or less. On the other hand, it was confirmed that the stirring time of Comparative Example 1-1, which used distilled water of 25°C as a solvent, was 16 hours, indicating a significant increase in the time required for stirring.

[0116] Figure 1 is an SEM cross-sectional image of a hydrogel according to Examples 1-3, Comparative Examples 1-1 and 2-1.

[0117] Specifically, FIG. 1a is an SEM cross-sectional image of a hydrogel according to Examples 1-3.

[0118] Figure 1b is an SEM cross-sectional image of a hydrogel according to Comparative Example 1-1.

[0119] Fig. 1c is an SEM cross-sectional image of a hydrogel according to Comparative Example 2-1.

[0120] Referring to Fig. 1, it can be seen that the hydrogels according to Example 1-3 and Comparative Example 1-1, which were stirred using a vacuum stirring degassing machine, produced significantly less bubbles, whereas Comparative Example 2-1, which was not stirred using a vacuum stirring degassing machine, produced an excessive amount of bubbles.

[0121] In addition, although the viscosity of the carboxymethyl cellulose used in Examples 1-3 is 3,000 cPs, which is higher than the viscosity of the carboxymethyl cellulose used in Comparative Examples 1-1 and 2-1 (1,000 cPs), the amount of bubbles generated is significantly lower compared to Comparative Example 1-1, in which distilled water at 25°C was used as a solvent. This confirms that a hydrogel with excellent physical properties was formed by using distilled water at 40°C or higher as a solvent.

[0123] Experimental Example 2. Evaluation of Water Absorption Amount

[0124] The water absorption amount of the eco-friendly cellulose-based superabsorbent hydrogel prepared in Example 1-1 was measured as follows.

[0125] The hydrogel prepared in Example 1-1 was completely dried, and after measuring the mass of the dried hydrogel, it was immersed in distilled water for 24 hours. Afterward, the hydrogel was removed and the dripping water was removed for 5 minutes, and then the amount of water absorbed was calculated by measuring the mass of the hydrogel after 24 hours using Equation 1 above.

[0126] Subsequently, the water absorption amount of the hydrogels prepared in Examples 1-2 to 1-4 and Example 2-1 was calculated using the same method, and the calculated water absorption amounts are shown in Table 2 below.

[0128] Water absorption amount (g / g) after 24 hours Example 1-1 205 Examples 1-2 224 Examples 1-3 245 Examples 1-4 179 Example 2-1 247 Comparative Example 1-1 174 Comparative Example 2-1 199

[0130] Referring to Table 2 above, it was confirmed that the water absorption amount of the hydrogels prepared in Examples 1-1 to 1-4 and Example 2-1 after 24 hours was 179 g / g or more. Through this, it can be confirmed that the water retention capacity of the hydrogels prepared in Examples 1-1 to 1-4 and Example 2-1 is excellent. In particular, in the case of Example 1-1, which used distilled water at a temperature of 90 ℃ as the solvent, it was confirmed that the water absorption amount was significantly superior compared to Comparative Example 1-1, which used distilled water at a temperature of 25 ℃ as the solvent, even though the same carboxymethyl cellulose with a viscosity of 1,000 cPs was used. That is, the amount of water that can be absorbed per unit mass is large, which may mean that a 3D network structure was well formed through appropriate cross-linking.

[0131] In addition, in the case of Examples 1-4, the viscosity of the carboxymethyl cellulose used was 5,000 cPs, which is significantly higher than the viscosity of the carboxymethyl cellulose used in Comparative Example 1-1, which was 1,000 cPs. However, since the water absorption was superior compared to Comparative Example 1-1, it can be confirmed that more uniform cross-linking was formed by using distilled water at a temperature of 90 ℃ as a solvent.

[0133] Experimental Example 3. Evaluation of Gel Fraction

[0134] The gel fraction of the hydrogel prepared in Example 1-1 was measured as follows. 1 g (initial dry weight) of the hydrogel prepared in Example 1-1 was immersed in distilled water and stirred at 100 rpm for 24 hours in a shaking incubator (SI-30, Labhouse, Daejeon, Korea) at 25 ℃. Afterward, the portion dissolved in water in the form of a sol was removed by filtration using a glass microfiber filter (Whatman, 100 circles, Grade GF / A, 47 mm Diameter), and then dried at 105 ℃ for 48 hours. The weight of the dried hydrogel (residual dry weight) was measured, and the gel fraction was calculated according to Equation 2 below.

[0136]

[0138] In Equation 2 above, G is the cellulose gel fraction (%), and W d is the residual dry weight (g) of the hydrogel, and W i is the initial dry weight (g) of the hydrogel.

[0140] Subsequently, the gel fractions of the hydrogels prepared in Examples 1-2 to 2-1 and Comparative Examples 1-1 and 2-1 were calculated using the same method and are shown in Table 3 below.

[0142] Gel fraction (%) Example 1-1 75 Examples 1-2 76 Examples 1-3 86 Examples 1-4 79 Example 2-1 97 Comparative Example 1-1 62 Comparative Example 2-1 70

[0144] As shown in Table 3 above, the gel fraction of the hydrogels prepared in Examples 1-1 to 1-4 and Example 2-1 is 75% or higher, confirming that the hydrogels are strongly cross-linked. On the other hand, the gel fraction of the hydrogels prepared in Comparative Example 1-1 and Comparative Example 2-1 is 70% or lower, indicating that the proportion of uncross-linked polymers in the hydrogels is high, and that there is a possibility of partial dissolution when exposed to water for a long time.

Claims

Claim 1 A method for manufacturing an eco-friendly cellulose-based superabsorbent hydrogel, comprising: a step of preparing a cellulose suspension comprising a cellulose raw material including a cellulose-based derivative, an organic acid-based crosslinking agent, and a solvent; a step of preparing a cellulose pre-gel by stirring the cellulose suspension; and a step of preparing a hydrogel by irradiating the cellulose pre-gel with radiation, wherein the temperature of the solvent is 40°C or higher. Claim 2 A method for manufacturing an eco-friendly cellulose-based superabsorbent hydrogel, wherein, in claim 1, the radiation dose is 30 kGy or less. Claim 3 A method for manufacturing an eco-friendly cellulose-based superabsorbent hydrogel, wherein, in claim 1, the organic acid-based crosslinking agent comprises a carboxylic acid compound. Claim 4 A method for manufacturing an eco-friendly cellulose-based superabsorbent hydrogel, wherein, in claim 1, the stirring is performed using a vacuum stirring degassing machine. Claim 5 A method for manufacturing an eco-friendly cellulose-based superabsorbent hydrogel, wherein, in claim 4, the stirring is performed for more than 0 minutes and less than or equal to 300 minutes. Claim 6 A method for manufacturing an eco-friendly cellulose-based superabsorbent hydrogel, wherein, in claim 1, the cellulose derivative is carboxymethyl cellulose (CMC). Claim 7 A method for manufacturing an eco-friendly cellulose-based superabsorbent hydrogel, wherein, in claim 1, the viscosity of the cellulose-based derivative is 1,000 cPs or more and 10,000 cPs or less as measured according to the international standard ASTM / ISO 2555. Claim 8 A method for manufacturing an eco-friendly cellulose-based superabsorbent hydrogel, wherein, in claim 1, the content of the cellulose-based derivative is 5 parts by weight or more and 15 parts by weight or less per 100 parts by weight of the cellulose suspension, and the content of the organic acid-based crosslinking agent is greater than 0 parts by weight and less than or equal to 10 parts by weight per 100 parts by weight of the cellulose suspension. Claim 9 Eco-friendly cellulose-based superabsorbent hydrogel manufactured by the method according to claim 1. Claim 10 An eco-friendly cellulose-based superabsorbent hydrogel according to claim 9, having a moisture absorption capacity of 20 g / g or more and 300 g / g or less.

Images