JP6004333B2 - Method for obtaining stress-strain relationship of cellulose hydrogel - Google Patents

Description

  The present invention relates to a method for obtaining a stress-strain relationship of cellulose hydrogel.

  Cellulose hydrogel is used as a food because of its unique texture. Cellulose hydrogel is also expected to be used as an industrial material because it has elasticity and excellent mechanical strength. In these applications, it is required to accurately evaluate the characteristics of cellulose hydrogel. As a conventional evaluation method, a method of breaking cellulose and examining its viscoelasticity is known. However, according to this method, it was not possible to evaluate the entire properties of the gel because the fibers were disaggregated with a blender or the like. Patent Document 1 (Japanese Patent Application Laid-Open No. 2005-213353) discloses a method for evaluating the characteristics of the entire gel by deforming the gel at a constant speed (increasing strain) and measuring the stress generated at that time. ing.

JP 2005-211133 A

  The inventor preliminarily examined the method described in Patent Document 1 and found that the method cannot accurately evaluate cellulose hydrogel. In other words, there is a demand for a method for accurately evaluating cellulose hydrogel, but there is still no satisfactory method. In view of such circumstances, an object of the present invention is to provide a method for obtaining a stress-strain relationship of cellulose hydrogel.

The inventors have found that the above problem can be solved by giving the cellulose hydrogel with increasing pressure and measuring the strain generated in the cellulose hydrogel. That is, the said subject is solved by the following this invention.
[1] including a step A of applying pressure to one surface of a cellulose hydrogel having a pair of substantially parallel surfaces while increasing the pressure and measuring strain generated in the cellulose hydrogel;
A method for obtaining a stress-strain relationship of the cellulose hydrogel.
[2] The method further includes the step of _{applying a} pressure P to the surface of the cellulose hydrogel to obtain a time t _eq for the strain to reach equilibrium.
The step A is performed by adding a pressure P having the same magnitude after a lapse of time t from the application of the pressure P, and the t satisfies 0.1 seconds ≦ t ≦ t _eq , [1] the method of.
[3] The method according to [2], wherein the step A is performed by repeatedly adding a pressure P having the same magnitude after the time t has elapsed since the pressure P was applied.
[4] (1) A step of preparing a cellulose hydrogel a having a pair of substantially parallel surfaces,
(2) removing cellulose from the cellulose hydrogel a to prepare a cellulose aerogel, absorbing the cellulose aerogel to prepare the restored cellulose hydrogel b,
(3) The process of acquiring the stress-strain relationship of the cellulose hydrogel a by the method in any one of said [1]-[3],
(4) A step of acquiring a stress-strain relationship of the restored cellulose hydrogel b by the same method as the method selected in (3),
(5) a step of comparing the stress-strain relationship between the two,
A method for evaluating the restoring characteristics of the restored cellulose hydrogel b.

  The present invention can provide a method for obtaining the stress-strain relationship of cellulose hydrogel.

Stress strain curve obtained in Example 1 Stress strain curve obtained in Example 2 Stress strain curve obtained in Example 3 Stress strain curve obtained in Example 4 Stress strain curve obtained in Example 5 Stress strain curve obtained in Example 6 Stress strain curve obtained in Comparative Example 1

1. Method for obtaining stress-strain relationship The method for obtaining a stress-strain relationship according to the present invention is a strain generated in a cellulose hydrogel that is applied to one surface of a cellulose hydrogel having a pair of substantially parallel surfaces while increasing pressure. Step A is measured.

(1) Stress-strain relationship The stress-strain relationship is a correlation between the stress applied to an object and the resulting strain, and is usually expressed as a stress-strain curve.

(2) Cellulose hydrogel Cellulose hydrogel is a gel formed by holding water in pores in a three-dimensional network structure of cellulose fibers. In the present invention, any cellulose hydrogel can be used, but a cellulose hydrogel produced by a cellulose-producing bacterium is preferred for reasons such as easy availability and good texture. Such a cellulose hydrogel is sometimes referred to as a “bacterial cellulose hydrogel”. Known cellulose-producing bacteria can be used. For example, strains such as ATCC 23769, ATCC 10245, ATCC 35959, ATCC 10821, ATCC 7000017, Acetobacter xylinum FF-88 (FERM BP-4407) can be used. A well-known thing can also be used for a culture medium, for example, agar-like solid culture medium, a liquid culture medium (culture solution), etc. Examples of the culture solution include a culture solution containing corn steep liquor and fructose as main components and having a pH adjusted to about 5. The culture is preferably stationary culture.

  Further, the cellulose-producing bacterium is cultured in a medium comprising a liquid phase medium part present in the liquid phase and an air phase medium part present in the air phase, and the first hydro having a low fiber density derived from the liquid phase medium part. A cellulose hydrogel having a multilayer structure having a gel layer and a second hydrogel layer having a high fiber density derived from an air phase medium may be used. Such a cellulose hydrogel can be produced by the method described in Japanese Patent Application No. 2011-196480.

(3) Shape of cellulose hydrogel The cellulose airgel used in the present invention has a pair of substantially parallel surfaces. “Substantially parallel” means a state parallel or parallel. The state according to the parallel means, for example, a case where the minimum angle formed by the normal lines is greater than 0 ° and 5 ° or less on two opposing surfaces, and more preferably the upper limit of the angle is 3 ° or less. Say. Examples of the shape of such a cellulose hydrogel include a substantially cubic shape, a substantially rectangular parallelepiped shape, and a substantially cylindrical shape. A substantially cube is a shape that conforms to a cube. For example, the substantially cube includes a shape in which the angle formed between the surfaces is slightly deviated from a right angle or rounded, and a shape in which each side is substantially parallel. The same applies to a substantially rectangular parallelepiped. The same applies to a cylinder, and the substantially cylinder includes a shape whose bottom surface or top surface is an ellipse. Further, the substantially cylindrical and substantially rectangular parallelepiped includes a plate-like shape.

Although the dimension of the cellulose airgel used by this invention is not specifically limited, When handling property, a measurement precision, etc. are considered, when it is a substantially cube or a substantially rectangular parallelepiped, the length of one side may be 0.5-2.0 cm. Preferably, it is 1.3-1.5 cm. Arbitrary shaped cellulose airgel can be processed into a substantially cubic shape or the like.
Moreover, when a cellulose airgel is a substantially cylinder, it is preferable that the diameters of a bottom face and a top surface are 0.4-2.0 cm, and it is more preferable that it is 0.7-1.5 cm. The height is preferably 0.5 to 2.0 cm, and more preferably 1.3 to 1.5 cm.

(4) Pressure In step A, the pressure applied to the surface of the cellulose hydrogel is increased, and the strain generated at that time is measured. Although how to give a pressure is not limited, when workability | operativity is considered, it is preferable to mount a weight in the top | upper surface of a cellulose hydrogel. For example, the process A can be implemented by placing a weight on the top surface of the cellulose hydrogel and increasing the number thereof. Moreover, the process A can also be implemented by placing a container filled with a liquid such as water on the top surface of the cellulose hydrogel and increasing the liquid in the container.

When bacterial cellulose hydrogel is used as the cellulose aerogel, since the cellulose fibers are elongated in the direction in which the gel grows, it is preferable that the surface perpendicular to the fiber elongation direction is the top surface and pressure is applied to the surface. . The reason is considered as follows. The top surface is in contact with the gas phase during the production of the gel, and the fiber density is high, so that it is difficult for water to escape. On the other hand, since the side surface is a cut surface, water easily escapes, and the gel has a structure in which a plurality of layers parallel to the top surface are laminated. . Therefore, accurate strain can be obtained by applying pressure to the top surface from which water is difficult to escape.
Furthermore, when the cellulose hydrogel has a structure in which a layer having a low fiber density and a layer having a high fiber density are laminated, it is preferable that the layer having a high fiber density is the bottom surface. This is because if the layer having a low fiber density is used as the bottom surface, the bottom surface (base) tends to tilt when pressure is applied, and accurate strain measurement cannot be performed.

  In the present invention, it is more preferable to perform the step A by applying the pressure P having the same magnitude after the passage of time t since the application of the pressure P, and the pressure P having the same magnitude after the passage of time t after the application of the pressure P. It is particularly preferred to carry out step A by repeatedly giving In this case, a strain is generated in the cellulose hydrogel by the applied pressure P, and the strain increases with time and eventually becomes saturated (an equilibrium state is reached). When the pressure P is newly applied after reaching the equilibrium state, the strain of the cellulose hydrogel becomes larger, so that more accurate measurement is possible. However, since it takes a certain amount of time to reach the equilibrium state, the cellulose hydrogel is dried, resulting in a large error, and further reducing the working efficiency. Therefore, the time t (hereinafter also referred to as “interval”) is preferably equal to or less than the time for reaching the equilibrium state, that is, equal to or less than the time for relaxing the response to the pressure P.

  On the other hand, if the interval is too short, sufficient distortion does not occur and measurement error increases. Therefore, the interval is preferably equal to or longer than the time at which a certain amount of distortion occurs. In the present invention, this time is preferably 0.1 seconds. Specifically, 0.1 second is the minimum time for the deformation of the gel to be detected as a strain by the stimulation of the applied force, so accurate measurement is possible by setting the minimum value of the interval to this time. It becomes.

  That is, in the present invention, a new stimulus is applied after the applied stimulus (pressure) is relieved by the cellulose hydrogel, and a change in strain at that time is measured. Thus, it is considered that the change in strain of the cellulose hydrogel can be measured more accurately by repeating the cycle considering relaxation.

  In a preferred embodiment, the step A is performed by the scheme “P → t → P → t...”, And “P → t” is one cycle. The number of cycles varies depending on the properties of the gel to be measured, but is preferably 1 to 10 cycles, and more preferably 2 to 4 cycles.

The pressure P is preferably 0.01 to 10 (gf / cm ² ), more preferably ^{2 to} 6 (gf / cm ² ), and further preferably 2 to 4 (gf / cm ² ). The pressure P may be 0.02 to 0.04 (gf / cm ² ). 1 gf is 9.81 mN.

When step A is carried out by repeating the cycle as described above, the value of t _eq varies depending on the applied pressure. For example, when a weight of 5 gf is placed on the top surface of a substantially cubic cellulose hydrogel having a side of 1.3 cm, that is, when a pressure of 2.96 gf / cm ² is applied, the time t _{eq for} strain to reach equilibrium Is approximately 180 seconds. Similarly, when a 10 gf weight is placed, that is, when a pressure of 5.92 gf / cm ² is applied, the time t _{eq for} strain to reach equilibrium is approximately 240 seconds. Similarly, when a weight of 0.05 gf is placed, that is, when a pressure of 0.03 gf / cm ² is applied, the time t _{eq for} strain to reach equilibrium is approximately 2 seconds.

As described above, the minimum value of the interval is preferably 0.1 seconds. However, depending on the pressure, the longer the time, the greater the distortion that occurs, so the measurement accuracy improves. Therefore, the following preferable intervals exist depending on the applied pressure.
1) When P = 0.01 to 10 (gf / cm ² ), t = 0.1 to 300 (seconds)
2) When P = 2 to 6 (gf / cm ² ), t = 1 to 300 (seconds)
3) When P = 2 to 4 (gf / cm ² ), t = 100 to 180 (seconds)
4) When P = 0.02 to 0.04 (gf / cm ² ), t = 0.1-2 (seconds)
Among them, in consideration of workability and the like, in the case of 3), a combination where t = 100 to 150 (seconds) is more preferable, and a combination where t = 110 to 130 (seconds) is more preferable.

  Since the pressure is preferably applied to one entire surface of the cellulose hydrogel, when the pressure is applied using a weight, the size of the weight is preferably a size that covers the entire one surface of the cellulose hydrogel. .

  The conventional method described in Patent Document 1 is a method of measuring the stress generated at that time while applying strain to the hydrogel while increasing the strain. However, this method cannot obtain an accurate stress-strain relationship of cellulose hydrogel. Although this reason is not limited, it is thought that stress is insensitive to the difference in the internal structure of cellulose hydrogel. The following can also be considered. The water present inside forms a hydrogen bond with the hydroxyl group of the cellulose fiber, and the surface tension also acts between the water molecules. Since the network structure of cellulose hydrogel is fine, many of these forces work, and water is strongly constrained in the cellulose hydrogel. Therefore, even if the cellulose hydrogel is distorted, the water that has been bonded by these forces cannot be removed from the gel instantaneously, but once it begins to escape, the surface tension will exceed the limit value and it will be released all at once. The stress to be unstable is unstable. For this reason, it is considered that the method of measuring stress cannot accurately evaluate the difference in network structure.

2. Cellulose hydrogel restoration method evaluation method The stress strain relation acquisition method of the present invention can be applied to cellulose hydrogel restoration evaluation. When the cellulose hydrogel is dried, it can be made into a cellulose aerogel. When the cellulose aerogel is further absorbed, a cellulose hydrogel (hereinafter also referred to as “restored cellulose hydrogel”) is obtained again. However, the inventor has so far found that the properties of the regenerated cellulose hydrogel are not completely consistent with the properties of the original cellulose hydrogel. About the reason, the inventor has guessed that it is because a cellulose fiber adheres excessively when drying a cellulose hydrogel, and the adhesion is not eliminated when absorbing water. Therefore, if the restoration characteristics of the restored cellulose hydrogel can be evaluated with high accuracy, it can also contribute to the development of a cellulose hydrogel having excellent restoration properties.
By obtaining the stress-strain relationship between the cellulose hydrogel and the regenerated cellulose hydrogel by the method of the present invention and comparing them, the rehabilitation property of the cellulose hydrogel can be evaluated.

  Specifically, (1) a step of preparing a cellulose hydrogel a having a pair of substantially parallel surfaces, (2) a cellulose aerogel is prepared by removing water from the cellulose hydrogel a, and the cellulose aerogel is absorbed by water. Preparing the restored cellulose hydrogel b, (3) obtaining the stress-strain relationship of the cellulose hydrogel a by the method described in the previous section, and (4) restoring by the same method as selected in (3) above. The restoring property of the cellulose hydrogel can be evaluated through a step of obtaining the stress-strain relationship of the cellulose hydrogel b and (5) a step of comparing the stress-strain relationship between the two. Hereinafter, each step will be described.

(1) Step of preparing cellulose hydrogel a Cellulose hydrogel a may be prepared as described above. Specifically, the cellulose hydrogel a for obtaining the stress-strain relationship in the step (3) and the cellulose hydrogel a for preparing the raw material for the restored cellulose hydrogel b are prepared.

(2) Step of preparing restored cellulose hydrogel b In this step, first, water is removed from the cellulose hydrogel a to prepare a cellulose airgel. It is preferable to remove the water by drying. However, if it is simply dried, defects such as cracks in the cellulose hydrogel may occur. The reason for this is that the water present inside the cellulose hydrogel may undergo volume expansion during drying, and the strain generated thereby destroys the surface of the cellulose hydrogel that has already been dried and reduced in strength. it is conceivable that. In order to solve this problem, the inventors have developed a method of coating the surface of cellulose hydrogel with water before drying (see Japanese Patent Application No. 2010-020455). Therefore, it is preferable to perform drying in the same manner in the present invention.

  Examples of the drying method include freeze drying, vacuum drying, supercritical liquid drying, and subcritical liquid drying. Freeze-drying is drying performed by freezing water and sublimating. In the present invention, it is preferable to freeze-dry at a low temperature of 50 ° C. or lower under reduced pressure in order to avoid gel degradation. Specifically, it is preferable to freeze-dry at a temperature of −50 to −40 ° C. under a pressure of 15 to 25 Pa.

Vacuum drying is a drying that removes water under reduced pressure. In this invention, it is preferable to dry at the temperature of -40-100 degreeC under the pressure of 25 Pa-0.1 MPa.
Supercritical liquid drying is a method in which a solvent solution is heated by being supercritical or higher and then dried by gently discharging solvent vapor out of the system. Subcritical liquid drying is a method in which a solvent solution is brought into a subcritical state where the temperature and pressure are slightly lower than those of the supercritical state, and the solvent vapor is discharged out of the system.

  In the present invention, it is preferable to replace water in the cellulose hydrogel as it is or with ethanol, methanol, carbon dioxide or the like, and dry water or ethanol with supercritical liquid drying or subcritical liquid drying. For example, when ethanol is used, supercritical liquid drying can be performed at 6.38 MPa and 243 ° C. In the case of drying as it is without replacing water, it is preferable to carry out in a subcritical state because cellulose may be decomposed in a supercritical state. For example, it is preferable to set the temperature to 100 ° C. or higher at atmospheric pressure and to a temperature of 374.15 ° C. (647.30 K) or lower at 22.12 MPa.

Although drying time can be suitably adjusted with a dry state, it is preferable to carry out for about 24 to 72 hours.
Moreover, you may use for drying in the state which immersed 30-50 volume% of the cellulose hydrogel in water or the said aqueous solution.
In addition, as described in Japanese Patent Application No. 2012-195993 and Japanese Patent Application No. 2012-196000, cellulose hydrogel is immersed in an aqueous solution containing a disaccharide and subjected to processing such as providing perforations on the surface as necessary, followed by drying. May be. By doing in this way, the restoration | restoration cellulose hydrogel excellent in the restoration rate can be obtained.

  Next, the regenerated cellulose hydrogel b is obtained by absorbing the cellulose airgel thus prepared. The temperature at this time is preferably 0 to 100 ° C. Water absorption can be performed by immersing the processed cellulose airgel of the present invention in water or an aqueous solution at the above temperature. Moreover, as described in Japanese Patent Application No. 2012-195993, the cellulose aerogel may be subjected to processing such as cutting the surface and then absorbed. By doing so, the restoration rate can be increased.

(3) Step of obtaining stress-strain relationship of cellulose hydrogel a According to the method described above, the stress-strain relationship of cellulose hydrogel a is obtained.

(4) Step of acquiring stress-strain relationship of regenerated cellulose hydrogel b By the same method as the method used in step (3), the stress-strain relationship of regenerated cellulose hydrogel b is acquired.

(5) Comparison process The stress-strain curves obtained from both are compared. If the curves have the same shape, it can be seen that the internal structure of the restored cellulose hydrogel b is the same as the cellulose hydrogel a used as a raw material. Conversely, when the shapes of the curves are different, it can be seen that the internal structure of the restored cellulose hydrogel b is different from the original cellulose hydrogel a.
The resilience can also be evaluated by the similarity of curves. Restorability is an index representing how close the shape and properties of the restored cellulose hydrogel are to the original cellulose hydrogel. Restorability can be evaluated using the restoration rate, and the restoration rate is defined by the mass of the restored cellulose hydrogel / the mass of the cellulose airgel.

[Example 1-1] Pressure P: 4.4 gf / cm ² , interval t: 15 seconds After preparing a cubic cellulose hydrogel (Natadecoko manufactured by Tsurami Co., Ltd.) having a side of 1.5 cm and thoroughly washing with water. And washed 20 times with hot water at 80 ° C.
The cellulose hydrogel of the same lot is loaded into a freeze dryer (Tokyo Science Instruments Co., Ltd., FDU-1200), and in this state, freeze drying (Tokyo Rika Instruments Co., Ltd., FDU-1200) is used to make −50 to It lyophilized | freeze-dried for 24 hours on the conditions of -40 degreeC and 15-25Pa, and obtained the cellulose airgel.
The cellulose airgel was immersed in water at 25 ° C. to obtain a regenerated cellulose hydrogel. Furthermore, the restoration cellulose hydrogel which has a different restoration | restoration rate was obtained by adjusting the time immersed in water. As described above, the restoration rate was obtained from the mass of the restored cellulose hydrogel / the mass of the cellulose airgel. The restoration rate of the obtained plurality of restored cellulose hydrogels was 0.20 to 0.36.

A 10 g weight (manufactured by Murakami Seiki Seisakusho Co., Ltd.) was placed on the top surface of the raw material cellulose hydrogel, and the time t _eq for strain to reach equilibrium was determined. t _eq was 180 seconds. The pressure with a 10 g weight was 4.4 gf / cm ² .

  A 10 g weight was added at 15-second intervals on the top surface of the raw material cellulose hydrogel of the same lot. That is, a new 10 g weight was repeatedly placed 15 seconds after the first weight was placed. And every 15 second progress, the height of the gel was measured and distortion was calculated | required. The strain was determined from (height before deformation−height after deformation) / (height before deformation).

A similar test was performed on a plurality of regenerated cellulose hydrogels, and an average value of strain was obtained. The interval t (seconds) satisfied the relationship of 0.1 ≦ t ≦ t _eq . The stress-strain curve thus obtained is shown in FIG. 1A.

[Example 1-2] Pressure P: 4.4 gf / cm ² , interval t: 60 seconds Evaluation was performed in the same manner as in Example 1-1 except that the interval t was set to 60 seconds. The results are shown in FIG. 1B.

[Example 1-3] Pressure P: 4.4 gf / cm ² , interval t: 120 seconds Evaluation was performed in the same manner as in Example 1-1 except that the interval t was set to 120 seconds. The results are shown in FIG. 1C.
From these results, it is clear that the stress-strain curve obtained in the present invention reflects the characteristics of the restored cellulose hydrogel.

[Example 2] Pressure P: 4.4 gf / cm ² , interval t: 120 seconds In the same manner as in Example 1, cellulose hydrogels having various restoration ratios (0.18 to 0.75) were prepared. Each restored cellulose hydrogel was tested under the same conditions as in Example 1-3 (pressure P: 4.4 gf / cm ² , interval t: 120 seconds) to obtain a stress strain curve. The results with restoration rates of 0.24, 0.45, and 0.62 are extracted and shown in FIG. 2A. From this result, it can be seen that the difference in the restoration rate clearly appears in the difference in the stress strain curve.

Then, the stress stresses in strain curve ^{1mN / mm 2 (10.2gf / cm} 2), 4mN / mm 2 (40.8gf / cm 2), when it is 10mN / mm 2 (102gf / cm 2), The strain of each restored cellulose hydrogel was determined. The relationship between the distortion and the restoration rate is shown in FIGS. In this example, when the stress is 1 mN / mm ² (10.2 gf / cm ² ), the relationship between the strain and the recovery rate is substantially linear. Therefore, by measuring and comparing the strain at a stress of 1 mN / mm ² (10.2 gf / cm ² ), the restoring characteristics of the restored cellulose hydrogel can be predicted to some extent.

[Example 3] Pressure P: 4.4 gf / cm ² , interval t: 120 seconds Similarly, a cellulose hydrogel having a restoration rate of 0.36 was prepared from the raw material of the same lot. The restored cellulose hydrogel contained a white balance (FIG. 3A). The white residue is produced as a result of the cellulose fibers agglomerating and insufficient water absorption. The restored cellulose hydrogel was tested under the same conditions as in Example 1-3 to obtain a stress strain curve. The results are shown in FIG. 3B. There was a staircase due to white residue.

[Example 4-1] Pressure P: 4.4 gf / cm ² , interval t: 15 seconds As a raw material cellulose hydrogel, a cubic cellulose hydrogel having a side of 1.5 cm (Natadecoko, manufactured by Tarami Co., Ltd.) was prepared. Further, a restored cellulose hydrogel having a restoration rate of 0.58 was prepared from the raw material cellulose hydrogel in the same manner as in Example 1-1.
The raw material cellulose hydrogel and the regenerated cellulose hydrogel thus obtained were tested in the same manner as in Example 1-1 to obtain a stress strain curve. However, the interval t was 15 seconds. The results are shown in FIG. 4A.

[Example 4-2] Pressure P: 4.4 gf / cm ² , interval t: 30 seconds The raw material cellulose hydrogel and regenerated cellulose hydrogel were the same as Example 4-1 except that the interval was set to 30 seconds. The stress strain curve was obtained. The results are shown in FIG. 4B.

[Example 4-3] Pressure P: 4.4 gf / cm ² , interval t: 120 seconds The raw material cellulose hydrogel and regenerated cellulose hydrogel were the same as Example 4-1 except that the interval was 120 seconds. The stress strain curve was obtained. The results are shown in FIG. 4C.

[Example 5-1] Pressure P: 2.2 gf / cm ² , interval t: 15 seconds As a raw material cellulose hydrogel, a cubic cellulose hydrogel having a side of 1.5 cm (Natadecoko, manufactured by Tarami Co., Ltd.) was prepared. Further, a restored cellulose hydrogel having a restoration rate of 0.60 was prepared from the raw material cellulose hydrogel in the same manner as in Example 1-1.
First, the raw material cellulose hydrogel and the regenerated cellulose hydrogel thus obtained were tested in the same manner as in Example 1-1 to obtain t _eq . However, a weight of 5 g was used for the weight. As a result, t _eq in the raw material cellulose hydrogel was 240 seconds, and t _eq in the _regenerated cellulose hydrogel was 240 seconds.
Next, a stress strain curve was obtained in the same manner as in Example 1-1. However, the interval t was 15 seconds. The result is shown in FIG. 5A.

[Example 5-2] Pressure P: 2.2 gf / cm ² , interval t: 60 seconds Raw material cellulose hydrogel and regenerated cellulose hydrogel were the same as Example 5-1 except that the interval was set to 60 seconds. The stress strain curve was obtained. The result is shown in FIG. 5B.

[Example 5-3] Pressure P: 2.2 gf / cm ² , interval t: 120 seconds Raw material cellulose hydrogel and regenerated cellulose hydrogel in the same manner as in Example 5-1, except that the interval was set to 120 seconds. The stress strain curve was obtained. The result is shown in FIG. 5C.

[Example 6-1] Pressure P: 0.02 gf / cm ² , interval t: 0.2 seconds Prepared as a raw material cellulose hydrogel is a cubic cellulose hydrogel having a side of 1.5 cm (Natadecoko, manufactured by Tarami Co., Ltd.). did. Further, a restored cellulose hydrogel having a restoration rate of 0.58 was prepared from the raw material cellulose hydrogel in the same manner as in Example 1-1.
A plastic container (length 20 mm, width 20 mm, height 50 mm) was placed on the top surface of the raw material cellulose hydrogel thus obtained. Using a dropping funnel, 0.05 mL of water was dropped into the container to apply pressure. The pressure was 0.02 gf / cm ² . However, since the mass of the plastic container was as light as 0.01 g, it was not regarded as pressure and ignored. The measured t _eq was 2 seconds.

  The plastic container was placed on the top surface of the raw material cellulose hydrogel of the same lot, and 0.05 mL of water was dropped into the container at 0.2 second intervals using a dropping funnel, and pressure was applied. The gel height was recorded with a video camera, and the gel height was measured every 0.2 seconds to determine the strain. The restored cellulose hydrogel was similarly tested to determine the strain.

[Example 6-2] Pressure P: 0.02 gf / cm ² , interval t: 0.9 seconds Except that the interval was set to 0.9 seconds, the raw material cellulose hydrogel and A stress-strain curve of the restored cellulose hydrogel was obtained. The result is shown in FIG. 6B.

[Example 6-3] Pressure P: 0.02 gf / cm ² , interval t: 1.25 seconds In the same manner as in Example 6-1 except that the interval was set to 1.25 seconds, the raw material cellulose hydrogel and A stress-strain curve of the restored cellulose hydrogel was obtained. The result is shown in FIG. 6C.
From the above, it is clear that the restorability of the restored cellulose hydrogel can be evaluated even at a low pressure of 0.02 gf / cm ² .

Comparative Example 1 Conventional Method The same raw material cellulose hydrogel as in Example 1-1 was prepared. The cellulose hydrogel was compressed at a rate of 10 mm / min using a small tabletop testing machine (EX-S, manufactured by Shimadzu Corporation) equipped with a 50 mm diameter circular plate and a 50 N load cell to obtain a stress strain curve. .
Subsequently, restored cellulose hydrogels having various restoration rates (0.25 to 0.45) were prepared in the same manner as in Example 1-1. The restored cellulose hydrogel was tested using the small tabletop testing machine to obtain a stress strain curve.

  As shown in FIG. 7, in the conventional method, the distinction between the curve of the raw material cellulose hydrogel and the curve of the restored cellulose hydrogel is not clear. The reason for this is considered to be that the stress is insensitive to the difference in the internal structure of the cellulose hydrogel as described above. Therefore, it is clear that the conventional method cannot evaluate the restoration characteristics of cellulose hydrogel.

Claims (7)

Including one or more surfaces of a cellulose hydrogel having a pair of substantially parallel surfaces while increasing the pressure, and measuring a strain generated in the cellulose hydrogel,
A method for obtaining a stress-strain relationship of the cellulose hydrogel ,
Further comprising the step of _applying pressure P to the surface of the cellulose hydrogel to obtain a time t _eq for the strain to reach equilibrium ,
A method in which the step A is carried out by adding a pressure P having the same magnitude after the time t has elapsed since the pressure P was applied, and the t satisfies 0.1 seconds ≦ t ≦ t _eq . The method according to claim 1 , wherein the step A is performed by repeatedly adding a pressure P having the same magnitude after the time t has elapsed since the pressure P was applied. It said pressure P is 0.01 to 10 (gf / cm ^2), wherein t is from 0.1 to 300 seconds, The method according to claim 1 or 2. It said pressure P is 2 to 6 (gf / cm ^2), wherein t is of 1 to 300 seconds, The method according to any one of claims 1 to 3. Said pressure P is 2 to 4 (gf / cm ^2), wherein t is of 100 to 180 seconds, The method according to any one of claims 1-4. Said pressure P is 0.02 to 0.04 (gf / cm ^2), wherein t is from 0.1 to 2 seconds, the method according to any one of claims 1 to 3. (1) preparing a cellulose hydrogel a having a pair of substantially parallel surfaces;
(2) removing cellulose from the cellulose hydrogel a to prepare a cellulose aerogel, absorbing the cellulose aerogel to prepare the restored cellulose hydrogel b,
(3) The process of acquiring the stress-strain relationship of the cellulose hydrogel a by the method in any one of Claims 1-6 ,
(4) A step of acquiring a stress-strain relationship of the restored cellulose hydrogel b by the same method as the method selected in (3),
(5) a step of comparing the stress-strain relationship between the two,
A method for evaluating the restoring characteristics of the restored cellulose hydrogel b.