Cellulose-based molded bodies and hydrogels and methods for their manufacture

Abstract

The method for producing the hydrogel of the present application includes: (A1) a step of preparing a treated object containing a water-soluble cellulose compound and water; (B1) a step of separating water from the treated object by heating the treated object; and (C1) a step of cooling the treated object whose cellulose compound content is increased by the treatment in step (B1), and repeating the series of steps from step (B1) to step (C1) until the cellulose compound content of the treated object reaches 10% by mass or more.

Description

Technical Field

[0001] This invention relates to cellulose-based molded articles and hydrogels, as well as methods for manufacturing them. Background Technology

[0002] In recent years, marine pollution caused by petroleum-derived plastics has become increasingly apparent. Biodegradable plastics, such as polylactic acid (PLA) and microbially produced polyesters, have gained attention as alternatives to petroleum-derived plastics. However, it has been pointed out that biodegradable plastics typically degrade more slowly in the ocean, potentially resulting in the same pollution as petroleum-derived plastics (e.g., accumulation in organisms or ingestion by animals).

[0003] Cellulose compounds, as edible polysaccharides, may become alternative materials to petroleum-derived plastics. Previous studies have explored the use of cellulose compounds to manufacture membranes or molded articles. For example, Patent Document 1 discloses a method for manufacturing molded articles by press molding cellulose powder. Patent Document 2 discloses a gas-permeable membrane utilizing the humidity-sensitive properties of regenerated cellulose.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 62-74609

[0007] Patent Document 2: Japanese Patent Application Publication No. 2015-208874 Summary of the Invention

[0008] The problem that the invention aims to solve

[0009] Cellophane is a film made of cellulose. It is relatively thin, about 50 μm thick, and transparent. However, a technology to manufacture cellophane with greater thickness while maintaining its transparency has not yet been established. For example, while the method described in Patent Document 1 can produce a molded body with a certain thickness, this molded body is not transparent.

[0010] This invention provides a cellulose-based molded article with a certain thickness and transparency, and a method for manufacturing the same. Additionally, this invention provides a hydrogel useful for manufacturing the aforementioned cellulose-based molded article, and a method for manufacturing the same.

[0011] Methods for solving problems

[0012] One aspect of the present invention relates to a method for manufacturing a hydrogel. The method includes the following steps, and repeats a series of steps (B1) to (C1) until the content of the cellulose compound in the treated material reaches 10% by mass or more.

[0013] (A1) Process for preparing a substance containing water-soluble cellulose compounds and water.

[0014] (B1) A process of separating water from a substance by heating it.

[0015] (C1) A process of cooling the processed material whose cellulose content has been increased by the treatment in step (B1).

[0016] According to this manufacturing method, a hydrogel containing water-soluble cellulose compounds and water, with the cellulose compound content being 10% by mass or more, can be obtained. This manufacturing method is based on the inventor's unique insight that by repeatedly performing a series of steps (B1) to (C1), the water content in the processed material can be gradually reduced, in other words, the cellulose compound content in the processed material can be gradually increased.

[0017] One aspect of the present invention relates to a method for manufacturing cellulose-based molded articles from the above-described hydrogel. The manufacturing method includes the following steps.

[0018] (a) The process of preparing the above-mentioned hydrogel

[0019] (b) The heating process performed while applying pressure to the molded hydrogel.

[0020] (c) The process of obtaining a cellulose-based molded body with a cellulose compound content of 95% or more by mass after heat treatment in step (b).

[0021] According to this manufacturing method, it is possible to obtain a cellulose-based molded body with a certain thickness (e.g., thickness of 0.5 mm or more), transparency (e.g., haze of less than 20%), and a cellulose compound content of 95% or more.

[0022] One aspect of the present invention relates to a method for manufacturing cellulose-based molded articles using an aqueous lithium bromide solution and cellulose. The manufacturing method includes the following steps.

[0023] (A2) A process of obtaining a cellulose-containing liquid by dissolving cellulose in an aqueous lithium bromide solution at a temperature above 100°C.

[0024] (B2) Process of obtaining molded articles from cellulose-containing liquids

[0025] (C2) Process of removing lithium bromide from the molded body by washing the molded body

[0026] (D2) The process of heating the molded body under pressure after lithium bromide removal.

[0027] (E2) The process of obtaining a cellulose-based molded body with a cellulose content of 95% or more by mass after heat treatment in process (D2).

[0028] According to this method, by heating the molded body after removing lithium bromide under pressure, it is possible to obtain a cellulose-based molded body with a certain thickness (e.g., thickness of 0.5 mm or more), transparency (e.g., haze of 50% or less), and a cellulose compound content of 95% or more.

[0029] Invention Effects

[0030] According to the present invention, a cellulose-based molded article having a certain thickness and transparency, and a method for manufacturing the same, can be provided. Furthermore, according to the present invention, a hydrogel useful for manufacturing the aforementioned cellulose-based molded article, and a method for manufacturing the same, can be provided. Attached Figure Description

[0031] Figure 1 A perspective view illustrating an example of a cellulose-based structure made of a cellulose-based molded body according to one embodiment of the present invention is shown for illustrative purposes.

[0032] Figure 2 This diagram illustrates an example of a process in which the content of methylcellulose (a cellulose compound) in the treated material gradually increases. Detailed Implementation

[0033] The following provides a detailed description of several embodiments of the present invention. The present invention is not limited to the embodiments described below. It should be noted that in the numerical ranges described in stages in this specification, the upper or lower limit of the numerical range for one stage can be replaced with the upper or lower limit of the numerical range for another stage. The upper or lower limit of the numerical ranges described in this specification can be replaced with the values ​​shown in the examples. In this application specification, hydrogel refers to a composition containing an aqueous dispersion system and is in a solid state.

[0034] [First Implementation Method]

[0035] (Hydrogels and their manufacturing methods)

[0036] The method for manufacturing the hydrogel according to this embodiment includes the following steps, and steps (B1) to (C1) are repeated until the content of cellulose compounds in the treated material reaches 10% by mass or more.

[0037] (A1) Process for preparing a substance containing water-soluble cellulose compounds and water.

[0038] (B1) A process of separating water from a substance by heating it.

[0039] (C1) A process of cooling the processed material whose cellulose content has been increased by the treatment in step (B1).

[0040] The following describes each process and the hydrogel produced.

[0041] <Process (A1)>

[0042] Process (A1) is a process for preparing a substance containing a water-soluble cellulose compound and water. The water-soluble cellulose compound is a compound that dissolves in 0.5 parts by mass or more of water at 25°C, and in which some or all of the hydrogen atoms of the hydroxyl groups in the cellulose are replaced by substituents other than hydrogen atoms. Examples of such cellulose compounds include methylcellulose and hydroxypropyl methylcellulose (HPMC). Well-known products can be appropriately used for methylcellulose and hydroxypropyl methylcellulose. Examples of commercially available methylcellulose include "METOLOSE MCE-4000 for Food Additives" manufactured by Shin-Etsu Chemical Industry Co., Ltd. Examples of commercially available hydroxypropyl methylcellulose include "METOLOSE SFE-4000 for Food Additives" manufactured by Shin-Etsu Chemical Industry Co., Ltd.

[0043] From the viewpoint of promoting phase separation when the processed material is heated, the degree of substitution of the water-soluble cellulose compound is preferably 45% or more, more preferably 60% or more. From the viewpoint of improving solubility in water, the degree of substitution of the water-soluble cellulose compound is preferably 65% ​​or less, more preferably 63% or less. It should be noted that, in this application specification, the degree of substitution of the water-soluble cellulose compound refers to the ratio of the introduced substituents in the cellulose compound to the total amount of hydroxyl groups and the introduced substituents.

[0044] There are no particular limitations on the weight-average molecular weight of water-soluble cellulose compounds, for example, it can be between 100,000 and 200,000. In this application specification, the weight-average molecular weight refers to the weight-average molecular weight calculated using the GPC method for standard polystyrene.

[0045] The content of water-soluble cellulosic compounds in the processed material prepared in this process is not particularly limited, for example, it is 0.5% to 4.0% by mass based on the total amount of the processed material. The processed material may contain components other than water-soluble cellulosic compounds and water. Examples of such components include, for instance, carbon nanofibers. The content of such components is not particularly limited, for example, it is 0.01% to 15% by mass based on the total amount of the processed material.

[0046] There are no particular limitations on the preparation method of the substance to be treated. For example, it can be obtained by mixing a water-soluble cellulose compound with water and other components other than the water-soluble cellulose compound and water, as needed. There are no particular limitations on the mixing means; for example, a magnetic stirrer can be used.

[0047] <Process (B1)>

[0048] Step (B1) is a step in separating water from the workpiece by heating it. By heating the workpiece, the phases of the workpiece separate into a gel containing cellulose compounds and water. There are no particular limitations on the heating temperature of the workpiece, as long as it allows phase separation into a gel containing cellulose compounds and water to occur; for example, it can be 60–150°C, or 80–120°C. There are no particular limitations on the heating time of the workpiece; for example, it can be 0.5–24 hours.

[0049] In step (B1), the material to be treated can be heated while contained within a container. This allows water to be separated from the material after phase separation into a gel containing cellulose compounds and water, by draining the water from the container. When heating the material while it is contained within a container, it is preferable that the container be sealed to prevent the surface of the resulting gel containing cellulose compounds from drying out. The heating method for the material is not particularly limited; an oven is an example.

[0050] <Process (C1)>

[0051] Step (C1) is a step of cooling the processed material whose cellulose content has been increased after the treatment in step (B1). The cooling temperature of the processed material is not particularly limited as long as it is the temperature at which the processed material becomes an aqueous solution or sol, for example, -10 to 25°C. The cooling time of the processed material is not particularly limited, for example, 0.5 to 24 hours. The cooling method of the processed material is not particularly limited; for example, a refrigerator can be used. The processed material can be cooled while contained in a container.

[0052] By repeating a series of steps from step (B1) to step (C1), the cellulose content of the processed material can be gradually increased (see reference). Figure 2 There is no particular limitation on the number of steps from step (B1) to step (C1), but from the viewpoint of increasing the content of cellulose compounds in the processed material, for example, 2 to 15 times or 2 to 5 times, preferably 4 times or more.

[0053] <Hydrogel>

[0054] According to the above manufacturing method, a hydrogel containing water-soluble cellulose compounds and water, with a cellulose compound content of 10% by mass or more, can be manufactured. From the viewpoint of lowering the phase transition temperature from gel to sol, the cellulose compound content in the hydrogel is preferably 10% by mass or more, more preferably 12.5% ​​by mass or more, and even more preferably 15% by mass or more. The compressive modulus of the hydrogel at 25°C is preferably 5 kPa or more, more preferably 10 kPa or more, and even more preferably 30 kPa or more. The compressive modulus refers to the value measured as the slope of the elastic region in a compression test using a mechanical testing machine at 25°C.

[0055] The hydrogel of this embodiment preferably has self-healing properties. In this specification, self-healing hydrogel means that even when the cut surfaces adhere after cutting the hydrogel, the compressive modulus and fracture strain of the hydrogel are at least 95% of the values ​​of the compressive modulus and fracture strain of the hydrogel before cutting. There are no particular limitations on the method for adhering the hydrogel; examples include the following: Distilled water or ion-exchanged water is applied to the cut surfaces of the hydrogel. Then, the hydrogel is fixed while the cut surfaces are adhered. The fixed hydrogel is cooled, and then heated. In this specification, the fracture strain of the hydrogel refers to the strain value measured as the strain value when the test piece breaks during a compression test using a mechanical testing machine at 25°C.

[0056] The phase transition temperature of the hydrogel from gel to sol in this embodiment is preferably 20°C or lower, more preferably 10°C or lower, and even more preferably 5°C or lower. In this specification, the phase transition temperature of the hydrogel from gel to sol can be determined by whether the object can be grasped by hand after being adjusted to a predetermined temperature.

[0057] (Cellulose-based molded articles and their manufacturing methods)

[0058] The method for manufacturing cellulose-based molded articles according to this embodiment includes the following steps.

[0059] (a) Steps for preparing the hydrogel of this embodiment

[0060] (b) The process of heating while applying pressure to the molded hydrogel.

[0061] (c) The process of obtaining a cellulose-based molded body with a cellulose compound content of 95% or more by mass after heat treatment in step (b).

[0062] The following describes each process and the resulting cellulose-based molded body.

[0063] <Process (a)>

[0064] Step (a) is the step of preparing the hydrogel of this embodiment. The hydrogel and its manufacturing method are described above.

[0065] <Process (b)>

[0066] Step (b) is a step of heating the hydrogel molded body while applying pressure. The hydrogel molded body can be obtained, for example, by cooling the hydrogel in a container or mold to change it into a fluid sol, and then heating it to change it into a gel.

[0067] The pressing pressure applied to the hydrogel molded body can be appropriately set according to the heating temperature and heating time, as described later. From the viewpoint of maintaining the smoothness of the surface of the heat-dried hydrogel and obtaining a dense cellulose-based molded body, the pressing pressure applied to the hydrogel molded body is, for example, 10 g / cm³. 2 The above can be 20-1000 g / cm³ 2 Or 30~100g / cm 2 The heating temperature of the hydrogel molded body can be appropriately set so that the content of cellulose compounds after heat treatment is above 95% by mass, for example, 60–150°C. The heating time of the hydrogel molded body can also be appropriately set so that the content of cellulose compounds after heat treatment is above 95% by mass, for example, 0.5–48 hours. There are no particular restrictions on the heating method for the hydrogel molded body; an oven is an example.

[0068] <Process (c)>

[0069] Step (c) is a process that obtains a cellulose-based molded body with a cellulose compound content of 95% by mass or more after the heat treatment in step (b). The cellulose compound content of the cellulose-based molded body is, for example, 95% by mass or more or 100% by mass. The water content of the cellulose-based molded body is, for example, 5% by mass or less, and can be 1% by mass or less or 0% by mass.

[0070] <Cellulose-based molded products>

[0071] According to the above manufacturing method, it is possible to manufacture cellulose-based molded articles with a thickness of 0.5 mm or more, a haze of less than 20%, and a cellulose compound content of 95% by mass or more. Examples of applications for cellulose-based molded articles include packaging materials, bundling materials, and structural materials. Examples of forms of cellulose-based molded articles include boards and articles with a specified shape. The thickness of the cellulose-based molded article can be appropriately set according to its application or form; for example, it can be 0.5 mm or more, or 1 to 5 mm or 1 to 10 mm.

[0072] The haze of the cellulose-based molded article is preferably 18% or less, more preferably 15% or less. In this application specification, the haze of the cellulose-based molded article refers to the value obtained by measuring the cellulose-based molded article with a thickness of 0.5 mm or more using a haze meter.

[0073] The total light transmittance of the cellulose-based molded article is preferably 60% or more, more preferably 75% or more. In this application specification, the total light transmittance of the cellulose-based molded article refers to the value calculated by measuring the incident light amount and the total transmitted light amount, and using the formula: Total transmittance = (Total transmitted light amount) / (Incident light amount) × 100. The incident light amount and the total transmitted light amount are values ​​measured using a haze meter.

[0074] The flexural modulus of the cellulose-based molded article is preferably 1 GPa or higher, more preferably 5 GPa or higher. In this application specification, the flexural modulus refers to the value measured using a three-point bending test on a mechanical testing machine.

[0075] (Cellulose-based structures and their manufacturing methods)

[0076] The cellulose-based structure of this embodiment can be obtained by preparing two or more of the above-described cellulose-based molded bodies, bonding them together, and then drying them thoroughly. More specifically, the cellulose-based structure of this embodiment is manufactured, for example, through the following steps: First, distilled water or deionized water is applied to the bonding portion of the cellulose-based molded bodies. The cellulose-based molded bodies are then bonded together using water. The bonded cellulose-based molded bodies are cooled to achieve adhesion. The cooled cellulose-based molded bodies are then heated to dry thoroughly.

[0077] The cellulose-based structures in this embodiment are, for example, containers and laminates. Figure 1 A three-dimensional view showing an example of a cellulose structure. Figure 1 The cellulose-based structure 10 shown is a container, composed of five cellulose-based molded bodies 1, 2, 3, 4, and 5. Cellulose-based molded bodies 1, 2, 3, and 4 form the sides of the container, and cellulose-based molded body 5 forms the bottom surface.

[0078] [Second Implementation]

[0079] (Cellulose-based molded articles and their manufacturing methods)

[0080] The first embodiment described above illustrates a method for preparing a hydrogel using a water-soluble cellulose compound and then manufacturing a cellulose-based molded article from the hydrogel. However, water-insoluble cellulose can also be used as a raw material. That is, the method for manufacturing a cellulose-based molded article according to this embodiment includes the following steps.

[0081] (A2) A process of obtaining a cellulose-containing liquid by dissolving cellulose in an aqueous lithium bromide solution at a temperature above 100°C.

[0082] (B2) Process of obtaining molded articles from cellulose-containing liquids

[0083] (C2) Process of removing lithium bromide from the molded body by washing the molded body

[0084] (D2) The process of heating the molded body under pressure after lithium bromide removal.

[0085] (E2) The process of obtaining a cellulose-based molded body with a cellulose content of 95% or more by mass after heat treatment in process (D2).

[0086] The following describes each process and the resulting cellulose-based molded body.

[0087] <Process (A2)>

[0088] Step (A2) involves dissolving cellulose in an aqueous lithium bromide solution at a temperature of 100°C or higher to obtain a cellulose-containing liquid. Known products can be used as the cellulose. Commercially available cellulose products include, for example, "BEMCOT" manufactured by Asahi Kasei Corporation. The weight-average molecular weight of the cellulose is not particularly limited, but is, for example, 5,000 to 1,500,000. The lithium bromide concentration in the aqueous lithium bromide solution is, for example, 55 to 60% by mass relative to the total amount of the aqueous lithium bromide solution, and can be 50 to 65% by mass.

[0089] The temperature at which cellulose is dissolved in the lithium bromide aqueous solution is, for example, 100–160°C, or 90–180°C. The amount of cellulose dissolved in the lithium bromide aqueous solution is, for example, 0.5–10 parts by mass relative to 100 parts by mass of the lithium bromide aqueous solution, or 0.1–25 parts by mass.

[0090] Cellulose-containing liquids may contain components other than cellulose, lithium bromide, and water. Examples of such components include, for instance, carbon nanofibers. The content of these components is, for example, 0.01 to 25% by mass, based on the total amount of the cellulose-containing liquid.

[0091] <Process (B2)>

[0092] Step (B2) is the process of obtaining a molded article from a cellulose-containing liquid. There are no particular limitations on the method of obtaining the molded article; for example, a method of cooling the cellulose-containing liquid, which is heated in step (A2), while it is directly contained in a container. The shape of such a container is not particularly limited and can be appropriately changed depending on the shape of the cellulose-based molded article being targeted. The temperature at which the cellulose-containing liquid is cooled is not particularly limited as long as it is the temperature at which the cellulose-containing liquid changes from the sol phase to the gel phase.

[0093] <Process (C2)>

[0094] Step (C2) is the process of removing lithium bromide from the molded body by washing it. There are no particular limitations on the washing solution used when washing the molded body, as long as it can remove lithium bromide from the molded body; examples include distilled water and deionized water. There are no particular limitations on the method of washing the molded body; examples include immersing the molded body in the aforementioned washing solution. For example, whether the molded body has been sufficiently washed can be determined based on the concentration of lithium bromide eluted into the washing water.

[0095] <Process (D2)>

[0096] Step (D2) is a heating process performed while applying pressure to the molded body after lithium bromide removal. The processing conditions and heating methods of step (D2) can be the same as those of step (b) in the first embodiment.

[0097] <Process (E2)>

[0098] Process (E2) is a process that, after the heat treatment in process (D2), yields a cellulose-based molded body with a cellulose content of 95% by mass or more. The cellulose content in the cellulose-based molded body can be 95% by mass or more, or 100% by mass. The water content in the cellulose-based molded body is, for example, 5% by mass or less, or 1% by mass or less, or 0% by mass.

[0099] <Cellulose-based molded products>

[0100] According to the above manufacturing method, it is possible to manufacture a cellulose-based molded article with a thickness of 0.5 mm or more, a haze of 50% or less, and a cellulose content of 95% by mass or more. The haze of the cellulose-based molded article of this embodiment is preferably 40% or less, more preferably 30% or less. Other physical properties and applications of the cellulose-based molded article of this embodiment are the same as those of the cellulose-based molded article of the first embodiment.

[0101] (Cellulose-based structures and their manufacturing methods)

[0102] The cellulose-based structure of this embodiment is obtained by preparing two or more of the above-described cellulose-based molded bodies and bonding them together. There are no particular limitations on the means of bonding the cellulose-based molded bodies; examples include woodworking adhesives and instant adhesives. The shape of the cellulose-based structure of this embodiment can be the same as the shape of the cellulose-based structure of the first embodiment.

[0103] Example

[0104] The present invention will be described in more detail below based on embodiments, but the present invention is not limited to the following embodiments.

[0105] The hydrogel and cellulose-based molded articles of the first embodiment were manufactured as described below.

[0106] [Hydrogel Manufacturing]

[0107] <Example 1a>

[0108] (Process (A1))

[0109] Powdered methylcellulose (manufactured by Shin-Etsu Chemical Industry Co., Ltd., trade name: "METOLOSE MCE-4000 for Food Additives"), a water-soluble cellulose compound, was dissolved in distilled water to prepare a treated sample containing 2% by mass of dissolved methylcellulose. Next, 1000g of the obtained treated sample was poured into a heat-resistant container (12cm long × 12cm wide × 10cm high).

[0110] (Process (B1))

[0111] The heat-resistant container containing the material to be treated was heated in an oven at 110°C for 3 hours, thereby causing the phase of the material to separate into methylcellulose gel and separated water. The separated water was then drained from the heat-resistant container.

[0112] (Process (C1))

[0113] The methylcellulose gel was allowed to cool naturally to room temperature. Then, it was cooled in a refrigerator at 4°C for 1 hour to obtain a treated product containing methylcellulose and water.

[0114] After step (A1), the material is processed seven times through steps (B1) and (C1) to obtain a hydrogel containing methylcellulose (8cm long × 8cm wide × 1cm thick). Figure 2 A graph showing the gradual increase in the methylcellulose content of the treated material is presented. The resulting hydrogel exhibits no cracking or fissures and has no flowability, thus remaining self-supporting and stable at room temperature (25°C). The resulting hydrogel is graspable by hand. The composition of the resulting hydrogel is shown in Table 1.

[0115] <Example 1b>

[0116] The material was treated four times in steps (B1) and (C1) instead of the seven times described above, and the hydrogel was otherwise obtained in the same manner as in Example 1a. The resulting hydrogel was free from cracking and fissures and had no flowability, thus remaining self-supporting and stable at room temperature (25°C). The resulting hydrogel was graspable by hand. The composition of the resulting hydrogel is shown in Table 1.

[0117] <Example 1c>

[0118] Hydroxypropyl methylcellulose (manufactured by Shin-Etsu Chemical Industry Co., Ltd., trade name: "METOLOSE SFE-4000 for Food Additives") was used instead of methylcellulose, and the hydrogel was obtained in the same manner as in Example 1a. The obtained hydrogel did not crack or fissure, nor did it have any flowability, and therefore remained self-supporting and stable at room temperature (25°C). The obtained hydrogel could be grasped by hand. The composition of the obtained hydrogel is shown in Table 1.

[0119] <Comparative Example 1a>

[0120] Instead of performing the treatment seven times, one process (B1) and one process (C1) were performed on the subject, otherwise the treatment was performed in the same manner as in Example 1a. The resulting treated product was a methylcellulose sol at room temperature (25°C) and did not form a hydrogel. The composition of the resulting treated product is shown in Table 1.

[0121] [Table 1]

[0122]

[0123] [Determination of the compressive modulus of hydrogels]

[0124] The hydrogel of the example was excavated to obtain cylindrical test pieces (25 mm in diameter × 10 mm in thickness). The compressive modulus of the obtained test pieces was measured at 25°C. The cylindrical test pieces were subjected to compression tests using a mechanical testing machine (manufactured by Shimadzu Corporation, trade name: "EZ-TEST"), thereby determining the compressive modulus. The compressive modulus of the hydrogel of Example 1a was 50 kPa.

[0125] [Determination of the storage modulus of hydrogels]

[0126] For the hydrogel of the example, the storage modulus was measured at 20°C, 40°C, and 60°C. A rheometer (Anton Paar MCR501) was used for the measurements. The measurement conditions were set as follows: heating rate 1°C / min, shear strain 0.001%, and frequency sweep (0.1–100 rad / s) mode. The storage moduli of the hydrogel of Example 1a at 20°C, 40°C, and 60°C were 30 kPa, 40 kPa, and 60 kPa, respectively.

[0127] [Evaluation of the self-healing properties of hydrogels]

[0128] Two cylindrical specimens (25 mm in diameter × 10 mm in thickness) were obtained by excavating the hydrogel of the example. One specimen was cut into two semi-cylinders. Then, distilled water was applied to the cut surfaces with a cotton swab. Afterward, the cut surfaces were pressed together and wrapped with PVC insulating tape around the outer periphery, thereby fixing the two semi-cylinders in an adhered state. The two fixed semi-cylinders were stored in a refrigerator at 4°C for 1 hour, and then heated in an oven at 110°C for 15 minutes. After heating, they were allowed to cool naturally at room temperature. After natural cooling, the cut surfaces of the two semi-cylinders were bonded together, forming the same shape as the other specimen that was not cut. In addition, the compressive modulus of the cut and bonded specimen and the uncut specimen were measured in the same manner as the compressive modulus of the hydrogel. In addition, the fracture strain at 25°C was measured for both specimens. The compressive modulus was determined by performing a compression test on the cylindrical specimens using a mechanical testing machine (manufactured by Shimadzu Corporation, trade name: "EZ-TEST"). If the compressive modulus and fracture strain of the cut and bonded specimen are more than 95% of the compressive modulus and fracture strain of the uncut specimen, the hydrogel is considered to have self-healing properties.

[0129] For the hydrogel of Example 1a, the compressive modulus of both the cut and bonded sample and the uncut sample was 50 kPa, and the fracture strain was 40%. That is, the hydrogel of Example 1a has self-healing properties.

[0130] [Determination of phase transition temperature of hydrogels]

[0131] The phase transition temperature of the hydrogel in the examples was determined by whether the object could be picked up by hand after the hydrogel was adjusted to a specified temperature. The phase transition temperatures of the hydrogels in Examples 1a and 1b were 10°C and 20°C, respectively.

[0132] [Manufacturing of Cellulose-Based Molded Articles]

[0133] The hydrogel of the embodiment is subjected to the following steps (b) and (c) to obtain a cellulose-based molded body.

[0134] (Process (b) and Process (c))

[0135] The hydrogels of each embodiment were contained in a container. Weights were placed on the upper surface of the hydrogel, separated by a plate, thereby applying a 30 g / cm³ pressure to the hydrogel. 2 The hydrogel was then dried in an oven heated to 110°C under pressure. This yielded a cellulose-based molded body (2 mm thick). The resulting cellulose-based molded body was free of cracks and fissures and was dense, with a density of 1.3 g / cm³. 3The methylcellulose content of the cellulosic molded articles in Examples 1a and 1b was 100% by mass.

[0136] [Determination of Haze in Cellulose Molded Products]

[0137] The haze in the thickness direction of the cellulose-based molded articles of each embodiment was measured. A haze meter HZ-V3 (device name, manufactured by Suga Testing Equipment Co., Ltd.) was used for the measurement. The measurement was performed in dual-beam mode (light source: C-beam). The haze of the cellulose-based molded articles of Examples 1a and 1b was 15%.

[0138] [Total light transmittance of cellulosic molded articles]

[0139] The total transmittance in the thickness direction of the cellulose-based molded articles of each embodiment was measured. Incident light and total transmitted light were measured, and the total transmittance was calculated in the form of total transmittance = (total transmitted light) / (incident light) × 100. A haze meter HZ-V3 (device name, manufactured by Suga Testing Equipment Co., Ltd.) was used for the measurement. The total transmittance of the cellulose-based molded articles of Examples 1a and 1b was 80%.

[0140] [Determination of Flexural Modulus of Cellulose Molded Articles]

[0141] For the cellulose-based molded articles of each embodiment, a three-point bending test was performed using a mechanical testing machine (manufactured by Shimadzu Corporation, trade name: "EZ-TEST") to determine the flexural modulus. The testing conditions were set as follows: distance between support points 40 mm and test speed 1 mm / min. The flexural modulus of the cellulose-based molded articles of Examples 1a and 1b was 2.5 GPa.

[0142] [Manufacturing of Cellulose Structures]

[0143] Five cellulose-based molded bodies from each embodiment were prepared, and distilled water was applied to the main surface of each cellulose-based molded body using a cotton swab. Next, the cellulose-based molded bodies were laminated together with their main surfaces facing each other, separated by water, thus stacking five cellulose-based molded bodies. Then, the laminated cellulose-based molded bodies were placed in a refrigerator at 4°C for 1 hour to bond them together. Afterward, the five cellulose-based molded bodies were heated in an oven at 110°C for 10 minutes until the bonding surfaces became cloudy. Next, the five cellulose-based molded bodies were clamped together with clips (alligator clips for stationery) with force applied perpendicular to the main surface of the cellulose-based molded bodies, and then heated in an oven at 110°C for 2 hours to dry them completely, thus obtaining a cellulose-based structure formed by bonding five cellulose-based molded bodies. Cellulose structures are 1 cm thick, unbroken and cracked, and dense, allowing them to be cut with a saw, drilled, and driven into nails.

[0144] The cellulose-based molded body and cellulose-based structure of the second embodiment described above are manufactured as follows.

[0145] [Manufacturing of Cellulose-Based Molded Articles]

[0146] <Example 2a>

[0147] Perform the following processes (A2) to (E2) to obtain a cellulose-based molded body.

[0148] (Process (A2))

[0149] Lithium bromide was dissolved in distilled water to prepare an aqueous solution of lithium bromide containing 60% by mass. The prepared lithium bromide aqueous solution was then dissolved with cellulose (manufactured by Asahi Kasei Corporation, trade name: "BEMCOT") at a concentration of 2% by mass, and the solution was heated and stirred at 120°C or higher to prepare a cellulose-containing liquid.

[0150] (Process (B2))

[0151] 700g of the obtained cellulose-containing liquid was injected into a heat-resistant container (12cm long × 12cm wide × 10cm high) and allowed to cool naturally at 25°C to obtain a gel-like shaped body.

[0152] (Process (C2))

[0153] The encapsulated lithium bromide is removed by washing the molded body after immersion in distilled water.

[0154] (Process (D2) and Process (E2))

[0155] The molded body, from which lithium bromide has been removed, is placed inside a container. Next, weights are placed on the upper surface of the molded body through a plate, thereby applying a 30 g / cm³ pressure. 2 The pressure was applied. Under this condition, the molded body was dried in an oven heated to 110°C until completely dry. This yielded a cellulose-based molded body (2 mm thick). The obtained cellulose-based molded body had a cellulose content of 100% by mass. The obtained cellulose-based molded body was free of cracks and fissures and was dense, with a density of 1.3 g / cm³. 3 .

[0156] [Determination of haze, total transmittance, and flexural modulus of cellulosic molded products]

[0157] The haze, total transmittance, and flexural modulus of the resulting cellulose-based molded articles were measured in the same manner as in Example 1a. The results showed a haze of 50%, a total transmittance of 75%, and a flexural modulus of 5.0 GPa.

[0158] [Manufacturing of Cellulose Structures]

[0159] Prepare five cellulose-based molded bodies and use them to assemble a box-shaped container with four sides and a bottom (see reference). Figure 1 That is, woodworking adhesive is applied to the contact points of the cellulosic molded parts using a cotton swab. Next, the five cellulosic molded parts are temporarily fixed with tape and left to cure until the woodworking adhesive hardens, thus obtaining a container. The resulting container is free from cracks and fissures, is dense, can be cut with a saw, can be drilled, and can be nailed.

[0160] Industrial availability

[0161] According to the present invention, a cellulose-based molded article having a certain thickness and transparency, and a method for manufacturing the same, can be provided. Furthermore, according to the present invention, a hydrogel useful for manufacturing the aforementioned cellulose-based molded article, and a method for manufacturing the same, can be provided.

[0162] Symbol Explanation

[0163] 1-5… Cellulose-based molded bodies, 10… Cellulose-based structural bodies.

Claims

1. A method for producing a hydrogel, comprising: (A1) a step of preparing a treated material containing a water-soluble cellulose-based compound and water; (B1) a step of separating water from the treated material by heating the treated material; and (C1) a step of cooling the treated material in which the content of the cellulose-based compound is increased by the treatment in step (B1), repeating the series of steps of steps (B1) to (C1) until the content of the cellulose-based compound of the treated material reaches 10 mass% or more, the water-soluble cellulose-based compound is a compound that dissolves 0.5 parts by mass or more with respect to 100 parts by mass of water at 25°C and in which part or all of hydrogen atoms of hydroxyl groups contained in cellulose are substituted with a substituent other than hydrogen atom.

2. The method for producing a hydrogel according to claim 1, wherein In step (B1), the treated material is heated while being housed in a container.

3. The method for producing a hydrogel according to claim 1 or 2, wherein, The cellulose-based compound is methyl cellulose.

4. A hydrogel containing a water-soluble cellulose-based compound and water, the content of the cellulose-based compound is 10 mass% or more, the water-soluble cellulose-based compound is a compound that dissolves 0.5 parts by mass or more with respect to 100 parts by mass of water at 25°C and in which part or all of hydrogen atoms of hydroxyl groups contained in cellulose are substituted with a substituent other than hydrogen atom, the water-soluble cellulose-based compound is at least one selected from the group consisting of methyl cellulose and hydroxypropyl methyl cellulose, the weight average molecular weight of the water-soluble cellulose-based compound is 100,000 to 200,000, a cellulose-based molded body in which the content of the cellulose-based compound is 95 mass% or more has a thickness of 0.5 mm or more, the phase transition temperature from gel to sol of the hydrogel is 20°C or less as determined by whether or not the object can be held by hand after the object is adjusted to a prescribed temperature, the hydrogel has self-repairability, which means that even in the case where the cut surface is adhered after the hydrogel is cut, the values of the compression modulus and the breaking strain of the hydrogel are 95% or more of the values of the compression modulus and the breaking strain of the hydrogel before the hydrogel is cut.

5. The hydrogel according to claim 4, which has a compression modulus of 5 kPa or more as measured as the slope of the elastic region in a compression test using a mechanical testing machine at 25°C.

6. A method for producing a cellulose-based molded body, comprising: (a) a step of preparing the hydrogel according to claim 4 or 5; (b) a step of performing heating while a press force is applied to a molded body of the hydrogel; and (c) a step of obtaining a cellulose-based molded body in which the content of the cellulose-based compound is 95 mass% or more by the heating treatment in step (b).

7. A cellulose-based molded body obtained by the method for producing a cellulose-based molded body according to claim 6, which has a thickness of 0.5 mm or more and has a haze of 20% or less, and in which the content of the cellulose-based compound is 95 mass% or more.

8. A method for producing a cellulose molded article, comprising: (A2) a step of obtaining a cellulose-containing liquid by dissolving cellulose in an aqueous lithium bromide solution at a temperature of 100°C or higher; (B2) a step of obtaining a molded article from the cellulose-containing liquid; (C2) a step of removing lithium bromide from the molded article by washing the molded article; (D2) a step of heating the molded article from which lithium bromide has been removed while applying a pressing force thereto; and (E2) a step of obtaining a cellulose molded article having a cellulose content of 95% by mass or more by the heating treatment of step (D2).

9. A cellulose molded article having a thickness of 0.5 mm or more and having a haze of 50% or less, and having a cellulose content of 95% by mass or more, which is obtained by the method for producing a cellulose molded article according to claim 8.

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