Thickening hydrogel crosslinked with natural component and preparation method therefor

Abstract

A hydrogel of one aspect has an excellent level of thickening performance even at a low concentration, has good dispersibility, has an outstanding level of water holding capacity compared to other thickeners, and has a non-sticky excellent feeling when used. In addition, the hydrogel not only has an excellent ability of dispersing nanoparticles, but also a production process therefor is relatively simple and does not require much energy. In addition, since the hydrogel is naturally crosslinked with citric acid, which is a naturally derived component, the hydrogel may be widely applied in the field of cosmetics pursuing green and clean beauty.

Description

Thickening hydrogel cross-linked with natural ingredients and method for manufacturing the same

[0001] The present application claims priority to Korean Patent Application No. 10-2024-0168919 filed on November 22, 2024, and the entire specification is a reference to the present application.

[0002] The present invention relates to a hydrogel for thickening crosslinked with natural ingredients and a method for manufacturing the same.

[0003] Recently, various natural-based materials are being used to replace petrochemical-based materials as thickening materials. In particular, cellulose nanofibrils, which are produced by mechanically nano-sizing plant-derived cellulose to have a size of less than 100 nm, are evaluated as one of the materials with high potential for use as thickening materials because they have a large surface area and abundant hydroxyl groups, resulting in excellent thickening power, strong resistance to salt and pH, and non-sticky properties.

[0004] However, since cellulose nanofibrils are particulate materials rather than polymeric electrolytes, their viscosity is affected not only by electrical repulsion but also by inter-particle interactions, and the relationship between concentration and viscosity is power-law. Consequently, viscosity increases exponentially as concentration increases, but tends to decrease significantly at low concentrations. In the case of thickening materials, it is important to effectively improve viscosity even with low addition amounts, but there are limitations to using cellulose nanofibrils as thickening materials in this regard.

[0005] As a result of diligent efforts to solve such problems, the inventors have developed a hydrogel utilizing cellulose nanofibrils that has a high level of thickening effect while maintaining an excellent level of thickening effect even at low concentrations.

[0006] One aspect provides a cross-linked hydrogel comprising cellulose nanofibrils and a cellulose-based polymer.

[0007] Another aspect provides a method for preparing a crosslinked hydrogel comprising the steps of: mixing a cellulose nanofibril solution and a cellulose-based polymer solution; adding citric acid and stirring; performing curing and aging; and washing.

[0008]

[0009] 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.

[0010] One aspect provides a hydrogel comprising cellulose nanofibrils and a cellulose-based polymer.

[0011] The above cellulose nanofibril solution may be in the form of a suspension, and may be a solution prepared using a method of mechanically decomposing cellulose under high pressure conditions to produce nano-sized cellulose nanofibrils or a chemical method of treating with an oxidizing agent, without any limitations on the method of processing naturally derived cellulose to nanometer size.

[0012] The cellulose nanofibrils of this specification may be CNF (cellulose nanofibrils) produced from various raw materials such as wood pulp, cotton pulp, and other non-wood pulp, although they are not limited thereto. They may be chemically untreated cellulose nanofibrils (UCNF), carboxymethylated cellulose nanofibrils (CMCNF), TEMPO-oxidized cellulose nanofibrils (TOCN), phosphated cellulose nanofibrils (PCNF), or cellulose nanocrystals (CNC) produced by strong acid hydrolysis of cellulose. Preferably, they may be carboxymethylated cellulose nanofibrils or TEMPO-oxidized cellulose nanofibrils with high viscosity. The above cellulose may be produced by the steps of: treating bleached kraft pulp derived from softwood or hardwood with TEMPO (2,2,6,6-tetramethyl piperidin-1-oxyl radical) catalytic oxidation; and nano-sizing the cellulose through mechanical treatment, but is not limited thereto.

[0013] The above-mentioned cellulose-based polymer solution corresponds to a solution in which a cellulose-based polymer made using cellulose and its derivatives is dissolved. The dissolved cellulose polymer may be an electrolyte. The types thereof may be carboxymethylcellulose or methylcellulose, and the above-mentioned carboxymethylcellulose may be selected from the group consisting of low viscosity carboxymethylcellulose, medium viscosity carboxymethylcellulose, and high viscosity carboxymethylcellulose, although it is not limited thereto. The molecular weight of the above cellulose-based polymer electrolyte may be 70,000 to 2,000,000 Da, 70,000 to 1,500,000 Da, 200,000 to 1,500,000 Da, 500,000 to 1,500,000 Da, 500,000 to 1,500,000 Da, 500,000 to 1,250,000 Da, 500,000 to 1,000,000 Da, or 600,000 to 800,000 Da, and preferably 700,000 Da.

[0014] In addition, the cellulose-based polymer may be included in an amount of 5 to 50% by weight, 5 to 40% by weight, 5 to 30% by weight, 5 to 25% by weight, or 10 to 25% by weight relative to the total weight of the nanofibrils, and preferably 20% by weight. If the weight ratio of the cellulose-based polymer is less than the above range, the thickening effect and the effect of improving dispersibility are insufficient, making it difficult to use as a thickener; if the content exceeds the above range, stickiness caused by the cellulose-based polymer electrolyte is induced, resulting in poor usability and failure to form a hydrogel well.

[0015] In the present specification, the crosslinking may be due to citric acid. The citric acid may be isolated and purified from a natural product, or may be produced by a biosynthetic or fermentation process using an intermediate derived from a natural product. Additionally, the citric acid may be included in an amount of 0.5 to 30% by weight, 0.5 to 25% by weight, 0.5 to 20% by weight, or 1 to 20% by weight, or 1 to 15% by weight relative to the total weight of the cellulose nanofibrils, and preferably 10% by weight. If the amount of citric acid administered is less than the above range, a hydrogel cannot be formed, and viscosity increases as the amount administered increases; however, if citric acid exceeding the above range is administered, the cellulose nanofibrils lose their water retention ability and viscosity decreases.

[0016] In this specification, water-holding capacity refers to the ability of a substance to absorb surrounding moisture and retain it.

[0017] Another aspect provides a thickening agent composition comprising the above-mentioned hydrogel.

[0018] As used herein, the term "thickener" refers to a substance that increases the viscosity of a solution, also known as a thickener, thickening stabilizer, or thickening agent. The thickener may be an aqueous thickener.

[0019] The cross-linked hydrogel may have a lattice structure. In this specification, the lattice structure refers to a state in which molecules form a regular lattice shape, meaning a form in which specific unit cells are repeatedly connected. This lattice shape is maintained through intermolecular interactions and may have a uniform spatial distribution and symmetry.

[0020] Another aspect provides a cosmetic composition comprising the above-mentioned hydrogel.

[0021] The above cosmetic composition may have, for example, a softening lotion, a nourishing lotion, a massage cream, a nourishing cream, an essence, a pack, a gel, an ampoule, or a skin-adhesive type cosmetic formulation.

[0022] The ingredients included in the above cosmetic composition may include ingredients commonly used in cosmetic compositions in addition to the above composition as active ingredients, and may include, for example, conventional auxiliary agents and carriers such as stabilizers, solubilizers, vitamins, pigments, and fragrances.

[0023] Another aspect provides a method for preparing a hydrogel comprising the steps of: mixing a cellulose nanofibril solution and a cellulose-based polymer solution; adding citric acid and stirring; and curing.

[0024] The method for manufacturing the hydrogel may further include an aging step. Additionally, the method for manufacturing the hydrogel may further include a degassing step and a washing step. Accordingly, the method for manufacturing the hydrogel may be a method for manufacturing the hydrogel comprising the steps of: mixing a cellulose nanofibril solution and a cellulose-based polymer solution; adding citric acid and stirring; degassing; performing curing and aging; and washing.

[0025] The stirring step may be performed using a stirrer or a high-pressure homogenizer, but is not limited to any specific method of stirring. The stirring may be performed for 10 to 120 minutes, 10 to 100 minutes, 10 to 60 minutes, 10 to 45 minutes, 15 to 45 minutes, or 20 to 40 minutes under conditions of 1000 to 10000 rpm, 1000 to 8000 rpm, 1000 to 6000 rpm, 1000 to 5000 rpm, 1000 to 4000 rpm, 1000 to 3000 rpm, 1000 to 2500 rpm, or 1500 to 2500 rpm, and preferably may be performed for 30 minutes, but is not limited thereto.

[0026] In the step of performing the curing and aging above, the curing step may be performed at 10 to 150 ℃, 10 to 130 ℃, 15 to 130 ℃, or 20 to 130 ℃, and preferably, may be performed for 0 to 120 minutes, 0 to 90 minutes, 0 to 80 minutes, or 0 to 70 minutes, or for 0 to 60 minutes, preferably for 30 minutes, under a temperature condition of 25 to 120 ℃. If curing is performed for a time exceeding the above range, the hydrogel is formed in the form of a film or a solid mass, making it difficult to use as a thickener.

[0027] Additionally, the aging step may be performed at a temperature of 15 to 50 ℃, 15 to 40 ℃, 15 to 35 ℃, 20 to 35 ℃, or 20 to 30 ℃, and preferably at a temperature of 25 ℃. Furthermore, the aging step may be carried out for 5 to 48 hours, 5 to 36 hours, 5 to 24 hours, 5 to 18 hours, 5 to 12 hours, or 6 to 12 hours under the above temperature conditions. If aging is carried out for a time shorter than the above range, a sufficient level of curing is not achieved, and if it exceeds the above range, excessive crosslinking occurs, making it difficult to use as a thickener.

[0028] The above curing and aging steps may be carried out in a sealed state to prevent the hydrogel from drying out during the process.

[0029] Another aspect provides a hydrogel manufactured by the above manufacturing method.

[0030] The hydrogel produced according to the method has an excellent level of thickening effect and maintains an excellent level of thickening effect even at low concentrations. In addition, it is very safe and eco-friendly because it is cross-linked using citric acid derived from nature, including citrus fruits.

[0031] Figure 1 is a flowchart showing the process for manufacturing a cross-linked hydrogel, a Latisgel thickener.

[0032] Figure 2 shows the viscosity of the hydrogel according to the amount of citric acid added.

[0033] Figure 3 is a figure showing the shape of the hydrogel according to the amount of citric acid added.

[0034] Figure 4 is a figure showing the viscosity according to temperature and time in the step of performing curing for a composition containing nanocellulose and citric acid.

[0035] Figure 5 shows the viscosity and turbidity of the hydrogel according to the type of cellulose-based polymer electrolyte.

[0036] Figure 6 is a figure confirming the viscosity and recovery effects while controlling the content of carboxymethylcellulose in a composition containing nanocellulose, citric acid, and carboxymethylcellulose.

[0037] Figure 7 is an FE-SEM image of the internal structure that varies depending on whether nanocellulose, citric acid, and carboxymethylcellulose are included.

[0038] Figure 8 is a figure showing the viscosity according to the concentration of the lattice gel thickener.

[0039] Figure 9 is a figure showing the turbidity of the lattice gel thickener depending on the presence or absence of carboxymethylcellulose (CMC).

[0040] Figure 10 is a figure showing the viscosity of a lattice gel thickener depending on whether or not TEMPO-catalyzed cellulose nanofibrils and carboxymethylcellulose were treated.

[0041] Figure 11 shows the results of evaluating the thixotropy of the Latis gel thickener using the ITT (3 interval thixotropy test) method.

[0042] Figure 12 is a figure comparing the particle dispersibility and dispersion stability of a lattice gel thickener with that of xanthan gum.

[0043] Figure 13 is a figure comparing the moisture retention level of a lattice gel thickener with that of a conventional commercially available product.

[0044] The present invention will be explained in more detail below through examples. However, these examples are intended to illustrate the invention and the scope of the invention is not limited to these examples.

[0045] As used herein, the singular form may include the plural form unless the context clearly indicates otherwise. Additionally, as used herein, “comprise, include” and / or “comprising, including” specify the presence of the mentioned features, numbers, steps, actions, parts, elements, and / or groups thereof, and do not exclude the presence or addition of one or more other features, numbers, actions, parts, elements, and / or groups.

[0046]

[0047] Examples

[0048] Example 1. Preparation of cross-linked cellulose nanofibrils

[0049] A hydrogel thickener containing cross-linked cellulose nanofibrils was prepared according to the flowchart shown in Fig. 1. The step of preparing the cross-linked thickener consists of: a step of preparing a mixture of a cellulose nanofibrils suspension and a cellulose-based polymer electrolyte (S110); a step of adding and stirring citric acid (S120); a degassing step (S130); a step of preparing a cross-linked hydrogel through curing and aging (S140); and a washing step (S150).

[0050] ① Preparation step of a mixture of cellulose nanofibril solution and cellulose-based polymer solution

[0051] The step (S110) of preparing the above cellulose nanofibrils suspension and cellulose-based polymer electrolyte mixture involves oxidizing bleached hardwood kraft pulp with TEMPO (2,2,6,6-tetramethyl piperidin-1-oxyl radical) catalyst, then mechanically processing the cellulose to nanoscale it, thereby preparing a 2% TEMPO-oxidized cellulose nanofibrils (hereinafter TOCN) suspension represented by the following chemical formula 1.

[0052] [Chemical Formula 1]

[0053]

[0054] As a cellulose polymer electrolyte to be mixed with this, carboxymethylcellulose (hereinafter CMC), represented by the following chemical formula 2 with a molecular weight of 700,000, was used.

[0055] [Chemical Formula 2]

[0056]

[0057] The above TOCN and CMC were each prepared at a concentration of 2%, and TOCN:CMC was mixed in a dry weight ratio of 80:20 to prepare 2% by weight relative to the total weight. To verify the effect according to the amount of CMC added, the physical properties were checked by adjusting the amount to 0 to 35% by weight based on the total solid content weight ratio of the composition.

[0058] To confirm the effect of cellulose-based polymer electrolytes having different molecular weights on cellulose nanofibrils, cellulose nanofibrils were further prepared using methylcellulose (MC), low viscosity carboxymethylcellulose (LCMC) with a molecular weight of 70,000 Da, and medium viscosity carboxymethylcellulose (MCMC) with a molecular weight of 250,000 Da as cellulose polymer electrolytes. The cellulose polymer electrolytes other than the above CMC were included at 20 wt%.

[0059]

[0060] ② Addition and stirring step of citric acid

[0061] In the step of adding and stirring citric acid (S120) above, citric acid represented by the following chemical formula 3 was added in powder form at a ratio of 0 to 100% relative to the solid content in the suspension.

[0062] [Chemical Formula 3]

[0063]

[0064] The suspension to which citric acid was administered was stirred with a stirrer at 2000 rpm for 30 minutes at room temperature.

[0065]

[0066] ③ Degassing stage

[0067] A degassing step (S130) was performed to remove air bubbles from the stirred suspension. Degassing was performed by degassing using a degassing mixer or by degassing using a vacuum degassing machine.

[0068]

[0069] ④ Crosslinking step through curing and aging

[0070] A curing and aging step (S140) was performed so that the suspension, after degassing, could be crosslinked. The suspension was cured at 25°C, 60°C, and 105°C for 30 minutes, and then aged at room temperature for 6 hours or more to produce a crosslinked hydrogel.

[0071]

[0072] ⑤ Washing step

[0073] A washing step (S150) was performed to remove impurities from the cross-linked hydrogel. Specifically, the hydrogel was left in distilled water for one day, and then the moisture on the surface was removed with an absorbent paper.

[0074]

[0075] Example 2. Confirmation of hydrogel characteristics according to the amount of citric acid added

[0076] To confirm the crosslinking and thickening effects according to the amount of citric acid added, citric acid was added to TOCN at a ratio of 0 to 100 wt% relative to the solid content of the suspension, cured at 105°C for 30 minutes, and aged for 12 hours to prepare a hydrogel. The prepared hydrogel was diluted to 1%, and then the viscosity was measured for 100 seconds using a Brookfield viscometer 63 spindle at a shear rate of 70 rpm. As a result, as shown in Figure 2, it was confirmed that viscosity increased with increasing citric acid content up to the amount of citric acid added being 0 to 10 wt% relative to the solid content of the suspension, but significantly decreased when 20 wt% of citric acid relative to TOCN was added. It was confirmed that when citric acid is added beyond the above range, excessive crosslinking occurs, causing the TOCN to aggregate and preventing sufficient dispersion.

[0077] In addition, when checking the shape of the hydrogel, as shown in Fig. 3, it was confirmed that a hydrogel is formed when citric acid is administered at 10% by weight, but when administered at 100% by weight relative to the solid content of the suspension, aggregation between fibers occurs in an opaque form and a hydrogel is not formed.

[0078]

[0079] Example 3. Confirmation of hydrogel viscosity according to curing and aging conditions

[0080] Experiments were conducted to establish optimal curing and aging conditions for a hydrogel prepared by adding 10 wt% citric acid relative to the solid content in the suspension. Specifically, while varying the temperature and time, viscosity was measured using a Bohlin rheometer at a shear rate of 1 s⁻¹ -1 Measurements were taken under the following conditions. As a result, as shown in Figure 4, it was confirmed that hydrogels prepared under conditions of high curing temperature and long aging time can have higher viscosity due to sufficient crosslinking. In addition, when cured under conditions of 150 degrees or higher, although the difference in viscosity increase was minimal, it was observed that the hydrogel dried out due to strong water evaporation. Regarding the aging time, it was confirmed that the increase in viscosity was minimal when performed for 30 minutes or less, while an appropriate viscosity could be achieved when performed for 6 hours or more.

[0081]

[0082] Example 4. Confirmation of viscosity and turbidity of hydrogel according to the type of cellulose-based polymer electrolyte

[0083] Hydrogels prepared by mixing a cellulose-based polymer electrolyte into a suspension at a concentration of 20 wt% relative to the solid content were diluted to a concentration of 0.5 or 1.0% to check viscosity and turbidity. As a result, as shown in Figure 5 (a), a significant improvement in viscosity was observed when CMC with a molecular weight above a certain level was added, while hydrogels with MC and LCMC having relatively low molecular weights showed low viscosity. Additionally, when comparing turbidity at a 1% concentration in Figure 5 (b), it was confirmed that turbidity actually increased when MC was added compared to before addition, whereas it decreased when CMC was added. It is determined that among cellulose-based polymer electrolytes with high molecular weight, using CMC with high anionicity improves dispersibility and reduces turbidity.

[0084]

[0085] Example 5. Confirmation of hydrogel viscosity according to the concentration of crosslinked hydrogel and the type of cellulose-based polymer electrolyte

[0086] Through the results of Example 4 above, it was confirmed that the composition containing CMC has the best viscosity. Based on these results, an experiment was conducted to determine the optimal CMC content. A composition mixed with TOCN and CMC in a 90:10 ratio was prepared as T_CMC10, and an example mixed in an 80:20 ratio was prepared as T_CMC20 (hereinafter referred to as the lattice gel thickener) to verify viscosity and recovery power.

[0087] As a result, as shown in Figure 6, it was confirmed that a composition containing TOCN, CA, and CMC showed a significantly higher level of viscosity and recovery than a composition containing only CA, and that the lattice gel thickener containing TOCN and CMC in a ratio of 80:20 showed the most optimal viscosity and recovery power. As the ratio of CMC increased, viscosity, dispersion, and recovery power increased, but it was confirmed that when more than 50% of CMC was included compared to TOCN, stickiness and shedding phenomena occurred severely during use.

[0088]

[0089] Example 6. Confirmation of hydrogel characteristics according to the type of cellulose polymer electrolyte

[0090] In order to confirm the characteristics of the compositions that vary according to their respective compositions, a composition containing only TOCN was named nanocellulose, a composition containing TOCN and CA was named crosslinking thickener, and a composition containing TOCN, CA, and CMC was named lattice gel thickener. As a result of photographing the interiors of the above compositions using FE-SEM (Field scanning electron microscopy), as shown in Fig. 7, it was confirmed that nanocellulose has an irregular and wide spatial structure, and the crosslinking thickener showed a dense spatial structure but still had an irregular structure, while the lattice gel thickener containing all of the above components formed a regular, uniform, and dense structure.

[0091]

[0092] Accordingly, as confirmed above, the hydrogel containing TOCN, CMC, and CA of the present invention can have dense and regular internal spaces, and thus is expected to have characteristics different from existing materials, so experiments were conducted on this.

[0093]

[0094] Example 7. Confirmation of characteristics of cross-linked hydrogel

[0095] 7-1. Check Viscosity

[0096] Experiments were conducted to determine the viscosity at different concentrations of the nanocellulose, crosslinking thickener, and lattice gel thickener prepared above, and the viscosity was determined using Brookfield. As a result, as shown in Figure 8, the lattice gel thickener composition containing TOCN, CMC, and CA showed the most significant level of viscosity, and it was confirmed that it exhibited a very high level of viscosity even in the low concentration range (0.4% or higher).

[0097] When the turbidity of the above compositions was checked, as shown in FIG. 9, it was confirmed that the lattice gel thickener composition containing all of the above components had less turbidity. This effect is expected to be due to the decrease in turbidity as the cohesiveness of the composition decreases as redispersibility increases.

[0098] To verify the actual viscosity level beyond the above experiment, hydrogels were applied to the back of the hand to check for stickiness. The stickiness performance of a TOCN hydrogel composed solely of TOCN, a lattice gel thickener mixed with TOCN and CMC in an 80:20 weight ratio, and a T_CMC40 hydrogel mixed with TOCN and CMC in a 60:40 weight ratio was compared with that of xanthan gum. The prepared hydrogels were prepared at a concentration of 2%. After applying the hydrogel to the back of the hand, pieces of paper were placed on top, and the stickiness level was determined by the number of remaining pieces of paper when the hand was turned over. As a result, as shown in Figure 11, xanthan gum, a commercial thickener, was found to be the most sticky. The lattice gel thickener (T_CMC20) showed lower stickiness than xanthan gum, providing a refreshing user experience, and was confirmed to have good spreadability.

[0099]

[0100] 7-2. Confirmation of thixotropy

[0101] To confirm the thixotropy of the hydrogel, a 3-interval thixotropy test (3ITT) was performed. As a result, as shown in Figure 11, the lattice gel thickener was observed to have a very high level of recovery power, returning to its original state after shearing.

[0102]

[0103] 7-3. Verification of Particle Dispersibility and Dispersion Stability

[0104] To compare the particle dispersibility and dispersion stability of the lattice thickening material, 0.1 g of graphene nanoplates were added to a 50 g solution of lattice gel thickener and xanthan gum diluted to 0.5%, and stirred at 2000 rpm for 10 minutes at a temperature of 25 ℃. That is, the graphene nanoplates were made to account for 0.2% of the total weight. When the dispersion stability of the graphene nanoparticles was checked immediately after stirring and after leaving for 2 weeks, it was confirmed that the lattice gel thickener had a significantly high level of dispersion uniformity, as shown in Figure 12.

[0105]

[0106] 7-4. Checking Water Retention Capacity

[0107] The water retention capacity of the lattice gel thickener was compared with that of natural polymer-based materials such as xanthan gum and carbomer. As a result, as shown in Figure 13, the lattice gel thickener demonstrated a water retention capacity comparable to that of carbomer and confirmed that it can retain a significantly higher level of moisture than xanthan gum, a commercially available thickener.

Claims

1. A hydrogel in which cellulose nanofibrils and cellulose-based polymers are cross-linked.

2. In Claim 1, The above-mentioned crosslinking is due to citric acid, in a hydrogel.

3. In Claim 2, A hydrogel in which the citric acid is included in an amount of 0.5 to 30 weight% based on the total weight of the cellulose nanofibrils.

4. In Claim 1, A hydrogel having a molecular weight of 70,000 to 1,500,000 Da of the above-mentioned cellulose-based polymer.

5. In Claim 1, The above cellulose-based polymer is carboxymethylcellulose or methylcellulose, and A hydrogel in which the above carboxymethylcellulose is one or more selected from the group consisting of low viscosity carboxymethylcellulose, medium viscosity carboxymethylcellulose, and high viscosity carboxymethylcellulose.

6. In Claim 1, A hydrogel in which the above-mentioned cellulose-based polymer is included in an amount of 5 to 50 weight% based on the total weight of the above-mentioned cellulose nanofibrils.

7. A thickening agent composition comprising a hydrogel according to any one of claims 1 to 6.

8. A cosmetic composition comprising a thickening agent composition according to Claim 7.

9. A step of preparing a hydrogel precursor solution by mixing a cellulose nanofibril solution and a cellulose-based polymer solution; A step of adding citric acid to the above hydrogel precursor solution and stirring; and A method for manufacturing a hydrogel comprising a curing step.

10. In Claim 9, A method for manufacturing a hydrogel, wherein the above manufacturing method further includes an aging step after the above curing step.

11. In Claim 9, A method for manufacturing a hydrogel, wherein the stirring step is performed at a temperature of 1,000 to 10,000 rpm.

12. In Claim 9, A method for preparing a hydrogel, wherein the curing step is performed at a temperature of 10 to 150 ℃ for 0 to 120 minutes.

13. In Claim 9, A method for preparing a hydrogel, wherein the aging step is performed at a temperature of 15 to 50 ℃ for 5 to 48 hours.

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