Sheet, method for manufacturing sheet, and mixed material

Abstract

To provide a sheet having high moisture absorption and high moisture desorption after moisture absorption.SOLUTION: A sheet includes a biomass nanofiber and polyalcohol. A mass ratio of the biomass nanofiber and the polyalcohol (polyalcohol / biomass nanofiber) is 15 / 85 to 75 / 25.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a sheet, a method for manufacturing the sheet, and a composite material. [Background technology]

[0002] Moisture absorbing and releasing materials are used in many aspects of daily life because they stabilize the humidity in the air and have a moisture regulating effect. For example, in clothing applications, sweat and moisture from the human body cause discomfort such as stuffiness and stickiness, but by quickly absorbing moisture inside the clothes and releasing it to the outside, the comfort of wearing them is improved. In addition, in residential applications, moisture absorbing and releasing materials can be used in the interior materials of homes to prevent condensation and maintain a comfortable humidity level of 40 to 60% for people. In addition, in air conditioning equipment, air conditioning systems that use desiccant materials to dehumidify the air consume less power than conventional dehumidification systems that use cooling condensation, so they are expected to have an energy-saving effect, and applicable moisture absorbing and releasing materials are in demand. In this way, materials that have both moisture absorbing and releasing properties are needed in many fields.

[0003] Examples of materials having both moisture absorbing and releasing properties include silica gel, synthetic zeolite, sodium sulfate, activated alumina, activated carbon, lithium chloride, calcium chloride, magnesium chloride, and phosphorus pentoxide.

[0004] Patent Document 1 proposes incorporating the above-mentioned materials together with pulp or fibers, or compounding them to form sheets. Patent Document 2 also proposes a sheet with moisture absorbing and releasing properties by mixing cellulose fibers or kapok fibers with synthetic fibers as a moisture absorbing and releasing material that utilizes natural fibers. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2019-058855 A [Patent Document 2] Patent Publication No. 2021-147722 Summary of the Invention [Problem to be solved by the invention]

[0006] However, inorganic materials such as silica gel described in Patent Document 1 have high moisture absorption capacity at low temperatures, but low moisture release capacity in low humidity environments, and once absorbed, they require heating at high temperatures to remove moisture. In addition, the sheet in Patent Document 2 has low moisture absorption and release capacity itself. In other words, neither of them can be said to be practical.

[0007] On the other hand, polyhydric alcohols such as glycerin, sorbitol, polyethylene glycol, butylene glycol, and dipropylene glycol are known as materials with high moisture absorption capacity. These polyhydric alcohols are used as raw materials for pharmaceuticals and cosmetics, and are generally used for moisturizing the skin. The properties of polyhydric alcohols are liquid or powder form, and an appropriate binder is required for molding. It is possible to mold them by combining them with resin, but by covering the surface with hydrophobic resin, the moisture absorption and desorption ability that they had in the past is lost, so it was difficult to process sheets that retain sufficient moisture absorption and desorption. In addition, regarding the moisture absorption and desorption of these polyhydric alcohols alone in liquid or powder form, the absolute amount of moisture absorption is high, but the moisture absorption and desorption speed is slow, so it took time to use them for humidity control purposes. For this reason, it can be said that it is difficult to use them for moisture absorption and desorption applications where a quick effect is required.

[0008] In view of the above, an object of the present invention is to provide a sheet having high moisture absorption and moisture release properties after absorbing moisture. [Means for solving the problem]

[0009] As a result of intensive research aimed at solving the above problems, the present inventors have come up with the following invention and found that the above problems can be solved.

[0010] [1] A sheet containing biomass nanofibers and a polyhydric alcohol, wherein the mass ratio of the biomass nanofibers to the polyhydric alcohol (polyhydric alcohol / biomass nanofibers) is 15 / 85 to 75 / 25. [2] The sheet according to [1], further comprising a wet strength agent. [3] The sheet according to [2], wherein the wet strength agent is contained in an amount of 0.5 to 15 parts by mass per 100 parts by mass of the biomass nanofibers. [4] The sheet according to any one of [1] to [3], wherein the biomass nanofibers have a viscosity average molecular weight of 50,000 or more. [5] The sheet described in any one of [1] to [4], wherein the biomass nanofibers are mechanically defibrated biomass nanofibers. [6] The sheet according to any one of [1] to [5], which has a moisture content of 15% by mass or more in a moisture absorption environment maintained at 25°C and 85% RH for 3 hours, and / or has a moisture content of 15% by mass or less in a moisture release environment maintained at 25°C and 85% RH for 3 hours and then at 25°C and 35% RH for 3 hours. [7] The sheet according to [6], wherein the difference between the moisture content in the moisture absorption environment and the moisture content in the moisture release environment is 10 mass% or more. [8] The sheet according to any one of [1] to [7], having a tensile strength of 5 MPa or more. [9] A method for producing a sheet, comprising mixing biomass nanofibers and a polyhydric alcohol so that the mass ratio of the biomass nanofibers to the polyhydric alcohol (polyhydric alcohol / biomass nanofibers) is 15 / 85 to 75 / 25.

[10] A mixed material for producing a sheet, comprising biomass nanofibers and a polyhydric alcohol, wherein the mass ratio of the biomass nanofibers to the polyhydric alcohol (polyhydric alcohol / biomass nanofibers) is 15 / 85 to 75 / 25. Effect of the Invention

[0011] According to the present invention, a sheet having high moisture absorption and moisture release properties after absorbing moisture can be provided. [Brief description of the drawings]

[0012] [Figure 1] 1 is a photograph showing the state of no shrinkage in the case where the sheet of the embodiment is produced. [Diagram 2] 1 is a photograph showing the state of little shrinkage in the case where the sheet of the embodiment is produced. [Diagram 3] 1 is a photograph showing the state of large shrinkage in the case where the sheet of the embodiment is produced or not. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Hereinafter, a sheet, a method for manufacturing the sheet, and a mixed material according to one embodiment (the present embodiment) of the present invention will be described.

[0014] Sheet The sheet according to the present embodiment contains biomass nanofibers and polyhydric alcohol, and the mass ratio of the biomass nanofibers to the polyhydric alcohol (polyhydric alcohol / biomass nanofibers) is 15 / 85 to 75 / 25. By containing the biomass nanofibers and the polyhydric alcohol in the above-mentioned predetermined ratio, a highly functional moisture absorbing and releasing sheet can be obtained that has both the moisture absorbing and releasing speed of the biomass nanofibers (particularly CNF) and the moisture absorbing and releasing amount of the polyhydric alcohol. That is, if the mass ratio is less than 15 / 85, the moisture absorption and moisture releasing properties after moisture absorption are low, and if it exceeds 75 / 25, it becomes difficult to form the sheet. The mass ratio is preferably 20 / 80 to 75 / 25, and more preferably 25 / 75 to 65 / 35.

[0015] (Biomass nanofiber) Biomass nanofibers can be uniformly dispersed and stabilized in water, and strong sheets can be obtained by coating and drying. Biomass nanofibers are dispersed in water and are highly hydrophilic, so they can be easily mixed with substances that have a high affinity for water, such as polyhydric alcohols and wet paper strength agents. Therefore, sheets can be easily produced by drying the prepared mixture. In addition, the sheet thickness can be controlled by adjusting the concentration and solid content of the dispersion. Among biomass nanofibers, cellulose in particular has good moisture absorption and release properties, and the moisture content increases to about 10% in a moisture-absorbing environment. The moisture absorption rate at this time is very fast, reaching equilibrium within 30 minutes in an environment of 20°C and 80% humidity.

[0016] The biomass nanofiber (BNF) according to the present embodiment is a nanofiber made of a biological polymer that is poorly soluble in water, and examples of such nanofibers include cellulose nanofiber, chitin nanofiber, chitosan nanofiber, silk nanofiber, etc. Among these, cellulose nanofiber (CNF) is preferred from the viewpoints of chemical stability, thermal stability, and cost.

[0017] The average fiber diameter of the biomass nanofibers is preferably 3 to 500 nm, more preferably 6 to 100 nm, even more preferably 7 to 50 nm, and even more preferably 8 to 25 nm, and of these, preferably 8 to 15 nm. The average length of the biomass nanofibers has an aspect ratio (average length / average fiber diameter) of 10 or more, and is preferably 0.5 to 100 μm, and more preferably 10 to 100 μm. The average fiber diameter and average length of biomass nanofibers can be calculated from the fiber diameter and length (approximately n = 20) measured based on electron microscope photographs taken at an appropriate magnification.

[0018] Biomass nanofibers are produced by a variety of methods, including mechanically defibrated biomass nanofibers produced by mechanical fiberization, and chemically modified biomass nanofibers obtained by chemically treating raw biomass to make it easier to pulverize, and then pulverizing it by mechanical fiberization.

[0019] Mechanically defibrated biomass nanofibers are produced using only the force of a water jet, resulting in less contamination with impurities than methods that use chemical modification. In addition, there is less loss in the degree of polymerization and crystallinity from the original raw material compared to methods that use chemical modification. Furthermore, there is an advantage to using fewer steps than methods that use chemical modification, such as no need for a washing process after chemical modification.

[0020] The viscosity average molecular weight of the biomass nanofiber according to this embodiment is preferably 50,000 or more, more preferably 70,000 to 170,000, and even more preferably 90,000 to 150,000. By having a viscosity average molecular weight of 50,000 or more, film-forming properties are improved, and a sheet without excessive shrinkage or cracks can be produced. Of the biomass nanofibers, the viscosity average molecular weight of CNF can be measured by the method described in the Examples below. For other than CNF, the viscosity average molecular weight is preferably 50,000 to 150,000 for chitosan nanofibers, and can be measured by dissolving in a 2% acetic acid / 0.3M sodium chloride aqueous solution. The viscosity average molecular weight of chitin nanofibers is preferably 50,000 to 150,000, and can be measured by first deacetylating the sample with sodium hydroxide to convert it into chitosan, and then dissolving it in a 2% acetic acid / 0.3M sodium chloride aqueous solution.

[0021] As described above, CNF is preferable for the biomass nanofibers according to this embodiment, and the CNF can be produced by known methods such as a method of subjecting the raw cellulose fibers to a micronization process or a method of synthesizing the CNF using bacteria such as acetic acid bacteria. Examples of the micronization process include a method using a water jet, a physical process (mechanical defibration) using a defibration device such as a high-pressure homogenizer, and a chemical process (chemical modification) that loosens the cellulose fibers by an oxidation reaction using an enzyme such as cellulase or a catalyst, and these processes can be used in combination.

[0022] Examples of raw cellulose fibers include wood pulps such as coniferous pulp and broadleaf pulp, cotton pulps such as cotton linters and cotton lint, non-wood pulps such as wheat straw, rice straw, rice husks, bagasse, bamboo, agricultural residues (vegetable waste, tea leaves, mandarin peel, etc.), herbaceous plants (Japanese silver grass, etc.), and seaweed, and these can be used alone or in combination of two or more.

[0023] The CNF may be one in which the hydroxyl groups of cellulose in the cellulose molecular chain are modified. Examples of such CNF include those in which the hydroxyl groups of cellulose are oxidized to carboxyl groups, esterified, etherified, or other functional groups are introduced into the cellulose fibers. From the viewpoint of improving the dispersibility of the CNF, the CNF may be anion-modified CNF in which an anionic group is introduced. Examples of the anionic group contained in the anion-modified CNF include an aldehyde group, a carboxyl group, a sulfate group, and a phosphate group.

[0024] Anion-modified CNF can be obtained by known methods such as a method of converting hydroxyl groups of cellulose into anionic groups by oxidation, or a method of reacting at least one selected from the group consisting of a compound having an anionic group, its acid anhydride, or a derivative thereof with the hydroxyl groups of cellulose. For example, there is a method of oxidizing the hydroxyl groups of cellulose by reacting an oxidizing agent such as sodium hypochlorite and a bromide such as sodium bromide using 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO) as a catalyst.

[0025] Since the longer the fiber length of CNF, the better the film-forming properties, the longer the fiber length is, and it is preferable to use CNF with a long fiber length that can be defibrated only by mechanical fiberization. Fiber length is correlated with molecular weight (viscosity average molecular weight), and CNF with a large viscosity average molecular weight is preferable.

[0026] (Polyhydric alcohol) Polyhydric alcohols have a strong affinity for water and are hygroscopic, so by including them in a specific ratio together with biomass nanofibers, good hygroscopicity can be achieved.

[0027] Furthermore, if a sheet is made by heating and drying only biomass nanofibers, strong shrinkage occurs during drying, making it difficult to obtain a smooth sheet. To produce a smooth sheet, it is necessary to remove moisture by ultrafiltration, and then dry the sheet by applying pressure from above using a special device. Another major issue with sheets made only of biomass nanofibers is that they are not flexible. In contrast, in this embodiment, the addition of a polyhydric alcohol gives plasticity to the biomass nanofibers, and a smooth and flexible sheet can be made without shrinkage by simply heating and drying.

[0028] In the present embodiment, the polyhydric alcohol refers to an alcohol having a hydric or higher valence, and examples thereof include dihydric alcohols, trihydric alcohols, tetrahydric alcohols, pentahydric alcohols, hexahydric or higher alcohols, and ethers thereof. A trihydric or higher alcohol or a polyether of a dihydric alcohol is preferable.

[0029] Examples of dihydric alcohols include C2 to C6 chain hydrocarbon diols, such as C2 to C6 glycols, for example, ethylene glycol, propylene glycol, dipropylene glycol, 1,3-butanediol, isoprene glycol, pentylene glycol, and hexylene glycol. Examples of the trihydric alcohol include the above-mentioned chain hydrocarbon triols, such as glycerin. The tetrahydric alcohol may, for example, be the chain hydrocarbon tetraol described above, such as pentaerythritol. Examples of the pentahydric or higher alcohol include xylitol and sorbitol. Examples of the ether include diethylene glycol, dipropylene glycol, diglycerin, triethylene glycol, tripropylene glycol, tetraethylene glycol, and tetrapropylene glycol.

[0030] From the viewpoint of moisture absorption capacity, the polyhydric alcohol of the present embodiment is preferably a trihydric alcohol or a dihydric alcohol, more preferably a trihydric alcohol, and even more preferably glycerin.

[0031] The equilibrium moisture content of polyhydric alcohols varies depending on the relative humidity of the environment, but for example, glycerin reaches a moisture content of over 50% after being left standing for four days in an environment of 20°C and 80% humidity, so the absolute amount of moisture absorption is very large. However, in an environment of 20°C and 80% humidity, the moisture content after one hour is only about 1.5%, so the moisture absorption rate may be slow, but the coexistence of biomass nanofibers increases the moisture absorption rate, and the sheet exhibits good moisture absorption and release properties.

[0032] (Wet strength agent) The sheet according to the present embodiment preferably further contains a wet strength agent. Both cellulose and polyhydric alcohol are highly hydrophilic, and there is concern that the strength of the sheet will decrease if the amount of moisture absorbed increases. For this reason, a wet strength agent used for sanitary paper (tissue paper, diapers, etc.), food packaging paper, filter paper, paper cups, processed base paper, and waterproof liners may be added.

[0033] The wet strength agent of the present embodiment is not particularly limited, and examples thereof include urea formaldehyde resin, melamine formaldehyde resin, polyamide polyamine epichlorohydrin resin, polyamide epoxy resin, vegetable gum, latex, polyethyleneimine, etc. Among these, polyamide epoxy resin is preferable. In addition to the wet strength agent, a paper strength enhancer such as glyoxal, gum, mannogalactan polyethyleneimine, polyacrylamide resin, polyvinyl alcohol, starch, carboxymethylcellulose, guar gum, urea resin, etc. may be used.

[0034] The wet strength agent is preferably 0.5 to 15 parts by mass, more preferably 0.8 to 13 parts by mass, per 100 parts by mass of biomass nanofibers. By using 0.5 to 15 parts by mass, water resistance can be improved and the sheet can be prevented from becoming too hard.

[0035] In the sheet according to this embodiment, the total of the biomass nanofibers and the polyhydric alcohol is preferably 60% by mass or more, more preferably 80% by mass or more, and even more preferably 85% by mass or more, in order to ensure the effects of the present invention. Ingredients other than biomass nanofibers and polyhydric alcohol include the wet strength agents already mentioned, but other ingredients such as polyvinyl alcohol (PVA) may also be included.

[0036] The polyvinyl alcohol is not particularly limited, and known polyvinyl alcohols can be used. In addition, the polyvinyl alcohol is produced by polymerizing a vinyl ester by a solution polymerization method, a bulk polymerization method, a suspension polymerization method, or the like according to a known method to obtain a polymer, and then saponifying the polymer. As the polyvinyl alcohol, only one type may be used, or two or more types may be used in combination.

[0037] Examples of the vinyl ester include vinyl acetate, vinyl formate, vinyl propionate, vinyl butyrate, vinyl pivalate, vinyl versatate, vinyl laurate, vinyl stearate, and vinyl benzoate.

[0038] The degree of polymerization of polyvinyl alcohol is not particularly limited, and commercially available products within the range can be used. For example, the degree of polymerization is preferably 100 to 4,000, more preferably 100 to 2,000, and even more preferably 100 to 1,000. The saponification degree of polyvinyl alcohol is preferably 80 mol % or more, and more preferably 90 mol % or more. The degree of polymerization of polyvinyl alcohol can be measured by a solution viscosity measurement method in accordance with JIS K6726:1994 (Testing method for polyvinyl alcohol). The degree of saponification can be determined in accordance with JIS K6726:1994.

[0039] Examples of commercially available polyvinyl alcohol products include Kuraray POVAL 5-88, Kuraray POVAL 22-88, Kuraray POVAL 30-88, and Kuraray POVAL 44-88 (all having a saponification degree of 88 mol%, manufactured by Kuraray Co., Ltd.), Kuraray POVAL 3-98, Kuraray POVAL 5-98, Kuraray POVAL 11-98, Kuraray POVAL 25-100, Kuraray POVAL 28-98, and Kuraray POVAL 60-98 (all having a saponification degree of 98 mol% or more, manufactured by Kuraray Co., Ltd.), GOHSENOL EG-05 and GOHSENOL EG-40 (all having a saponification degree of 88 mol%, manufactured by Nippon Synthetic Co., Ltd.), and GOHSENOL Z-100 and GOHSENOL Z-200 (all having a saponification degree of 98 mol% or more, manufactured by Nippon Synthetic Co., Ltd.).

[0040] The sheet according to this embodiment preferably contains 30% by mass or less of polyvinyl alcohol, more preferably 5 to 25% by mass, and even more preferably 7 to 20% by mass.

[0041] (Physical Properties) The sheet according to the present embodiment preferably has a moisture content of 15% by mass or more in a moisture absorption environment maintained at 25°C and 85% RH for 3 hours (hereinafter sometimes referred to as "moisture content in moisture absorption environment") and / or a moisture content of 15% by mass or less in a moisture release environment maintained at 25°C and 85% RH for 3 hours and then at 25°C and 35% RH for 3 hours (hereinafter sometimes referred to as "moisture release environment moisture content"). This allows the sheet to absorb and release moisture in rapid response to changes in humidity in the environment.

[0042] The moisture content of the hygroscopic environment is preferably 20% by mass or more, and the upper limit is practically about 60% by mass. The moisture release environment moisture content is preferably 11% by mass or less, and the lower limit is practically about 4% by mass.

[0043] The difference between the moisture content of the moisture absorbing environment and the moisture content of the moisture releasing environment is preferably 10% by mass or more, more preferably 15% by mass or more, with the upper limit being practically about 50% by mass. By making the difference 10% by mass or more, moisture can be absorbed and released in rapid response to changes in humidity in the environment.

[0044] The sheet according to the present embodiment has a tensile strength of preferably 5 MPa or more, more preferably 6 MPa or more, and even more preferably 10 MPa or more. By having a tensile strength of 5 MPa or more, it is possible to provide a sheet having excellent strength and ease of handling. The preferred upper limit of the tensile strength is not particularly limited, but in practice it is about 100 MPa.

[0045] From the viewpoint of productivity, the sheet according to this embodiment preferably has a thickness of 5 to 1000 μm, and more preferably 20 to 500 μm.

[0046] The sheet according to the present embodiment can be subjected to known processing, lamination, compounding, etc. as necessary and used in applications such as various types of clothing, interior materials for living spaces, moisture absorbing and releasing members used in air conditioning systems, moisture sensitive films for humidity sensors, etc.

[0047] [Method of manufacturing the sheet] The sheet manufacturing method according to this embodiment involves mixing biomass nanofibers and polyhydric alcohol so that the mass ratio of the biomass nanofibers to the polyhydric alcohol (polyhydric alcohol / biomass nanofibers) is 15 / 85 to 75 / 25, and forming the mixture into a sheet.

[0048] Specifically, biomass nanofibers, polyhydric alcohol, and an arbitrary wet paper strength agent were weighed out to a predetermined mass ratio in the solid content after drying, and mixed in a planetary centrifugal mixer at a revolution speed of 1000 to 2000 min. -1 The mixture is stirred and mixed for 3 to 30 minutes under conditions of 50% rotation speed (rotation speed is 50% of revolution speed). If air bubbles need to be removed, it is preferable to perform the stirring process under vacuum. The mixture is then placed in a specified container and dried to produce a sheet. Drying is preferably performed under conditions of 40 to 70°C for about 1 to 3 days.

[0049] [Mixed material] The mixed material of the sheet in this embodiment is a mixed material for producing a sheet, which contains biomass nanofibers and polyhydric alcohol, and has a mass ratio of the biomass nanofibers to the polyhydric alcohol (polyhydric alcohol / biomass nanofibers) of 15 / 85 to 75 / 25.

[0050] By containing biomass nanofibers and polyhydric alcohol in the aforementioned ratio, a highly functional moisture absorbing and releasing sheet material can be made that combines the moisture absorption and release speed of biomass nanofibers (especially CNF) with the moisture absorption and release amount of polyhydric alcohol.

[0051] Details of the biomass nanofibers, polyhydric alcohol, etc. are as described in the sheet according to this embodiment. In addition, when the wet strength agent, polyvinyl alcohol, etc. are contained, they are also as described in the sheet according to this embodiment. EXAMPLES

[0052] [Example 1] The CNF used was 5 wt% BiNFi-s RMa (manufactured by Sugino Machine, model: RMa-10005, viscosity average molecular weight 124,000, average fiber diameter 10 nm). The glycerin used was manufactured by Fujifilm Wako Pure Chemical Industries, and the wet strength agent used was polyamide epoxy resin (manufactured by Taoka Chemical Industry, model: Sumirez Resin 675A). The solids after drying were weighed out so that the mass ratio was CNF:glycerin:wet strength agent = 80:20:1, and the mixture was prepared by stirring and mixing for 10 minutes at a setting of 9 and with a vacuum in a planetary centrifugal mixer, Hi-Merge (Kyoritsu Seiki, HM-200WV). The mixture was then placed in a PFA dish and dried at 55°C for 2 days to prepare a sheet with a thickness of approximately 200 μm.

[0053] [Examples 2 to 10, Comparative Examples 1 to 4] A mixed material was prepared in the same manner as in Example 1, except that the mass ratio of CNF:glycerin:wet strength agent was changed as shown in Tables 1 and 2, and a sheet was produced. In addition, in Comparative Examples 3 and 4, it was not possible to produce a sheet.

[0054] [Example 11] A mixed material was prepared and a sheet was produced in the same manner as in Example 1, except that glycerin was replaced with polyethylene glycol (PEG300, Fujifilm Wako Pure Chemical Industries, Ltd.) and the mass ratio of CNF:polyethylene glycol:wet strength agent was changed as shown in Table 2.

[0055] [Example 12] A mixed material was prepared and a sheet was produced in the same manner as in Example 1, except that glycerin was replaced with 1,3-butanediol (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) and the mass ratio of CNF:1,3-butanediol:wet strength agent was changed as shown in Table 2.

[0056] [Example 13] A mixed material was prepared and a sheet was produced in the same manner as in Example 1, except that glycerin was replaced with isoprene glycol (Kuraray, Isoprene Glycol-S) and the mass ratio of CNF:isoprene glycol:wet strength agent was changed as shown in Table 2.

[0057] [Example 14] A mixed material and a sheet were produced in the same manner as in Example 1, except that 5 wt% BiNFi-sWFo (manufactured by Sugino Machine, model: WFo-10005, viscosity average molecular weight 105,000, average fiber diameter 10 nm) with a medium molecular weight was used instead of 5 wt% BiNFi-s RMa as the CNF, and the mass ratio of CNF:glycerin:wet strength agent was changed as shown in Table 2.

[0058] [Example 15] A mixed material and a sheet were prepared in the same manner as in Example 1, except that anion-modified CNF LeoCrysta (I-2SX, Daiichi Kogyo Seiyaku, average fiber diameter 3 nm) was used instead of 5 wt% BiNFi-s RMa as the CNF, and the mass ratio of CNF:glycerin:wet strength agent was changed as shown in Table 2.

[0059] [Examples 16 to 19] The CNF used was 5 wt% BiNFi-s RMa (manufactured by Sugino Machine, model: RMa-10005, viscosity average molecular weight 124,000, average fiber diameter 10 nm). The glycerin used was manufactured by Fujifilm Wako Pure Chemical Industries, and the wet strength agent used was polyamide epoxy resin (manufactured by Taoka Chemical Industry, model: Sumirez Resin 675A). The polyvinyl alcohol (PVA) used was manufactured by Fujifilm Wako Pure Chemical Industries (degree of polymerization: 1500-1800, fully saponified type). The mass ratio of CNF:glycerin:wet strength agent:PVA in the dried solid content was weighed out as shown in Table 2, and the mixture was mixed for 10 minutes with a setting of 9 and vacuum in a planetary centrifugal mixer, Hi-Merge (Kyoritsu Seiki, HM-200WV) to produce a mixed material. The mixed material was then placed in a PFA petri dish and dried at 55°C for 2 days to produce a sheet with a thickness of approximately 200 μm.

[0060] <Viscosity average molecular weight measurement> The viscosity average molecular weight of CNF was measured by a viscosity method. Specifically, the CNF aqueous dispersion was freeze-dried to obtain a dry powder sample, and then each cellulose fiber sample was dissolved in a copper ethylenediamine solution, and the intrinsic viscosity was calculated from the relative viscosity of the solution to the solvent using an Ostwald viscometer, and the molecular weight (viscosity average molecular weight) of each cellulose fiber was calculated.

[0061] <Whether or not the sheet can be made> The shape of the sheet obtained in each example was visually checked using a ruler and classified into the following four categories. The results are shown in Tables 1 and 2. No shrinkage: ◎, Small shrinkage: 〇, Large shrinkage: △, Cannot be made into sheets: × No shrinkage was defined as 90% or more of the entire sheet being smooth with almost no visible irregularities, as shown in Figure 1. Little shrinkage was defined as 80% or more of the entire sheet being smooth with less than 20% visible irregularities, as shown in Figure 2. Large shrinkage was defined as 20% or more of the entire sheet being uneven, as shown in Figure 3.

[0062] <Moisture absorption / desorption evaluation> The sheets obtained in each example were cut into pieces measuring 20 mm x 20 mm to prepare test pieces. The test pieces were dried by heating at 105°C for 2 hours, and the weight of the test pieces was measured in an absolutely dry state. After that, the test pieces were pre-conditioned in an environment of 25°C and 35% RH. Next, a thermohygrostat (manufactured by ESPEC, model: PSL-2J) was used to conduct a moisture absorption and desorption test on the sheet material in a specified temperature and humidity environment. First, the sheet was placed in an environment of 25°C and 85% RH, and the weight change after 3 hours was recorded to evaluate the moisture absorption characteristics of the sheet. Next, the sheet was placed in an environment of 25°C and 35% RH, and the moisture desorption characteristics of the sheet after 3 hours were evaluated. The results are shown in Tables 1 and 2.

[0063] <Mechanical property evaluation> From the sheets obtained in each example, a No. 8 tensile dumbbell-shaped test piece was cut out, and the sheet thickness was measured. The test pieces were then left to stand for 3 hours in a dry environment (25°C, 35% RH) and a wet environment (25°C, 70% RH), and then a tensile test was carried out. The tensile test was carried out at 25°C using a precision universal testing machine (Shimadzu Corporation, model: AG-50KNXD), and the tensile strength and strain (elongation) were measured. The test conditions were a test speed of 2 mm / min and a grip distance of 30 mm. The results are shown in Tables 1 and 2. In addition, in Comparative Examples 1 and 2, the shrinkage was too large, and there was no space to cut out a tensile test piece, so that it was not possible to prepare a test piece, and therefore measurement was not possible.

[0064] [Table 1]

[0065] [Table 2]

Claims

1. A sheet containing biomass nanofibers and a polyhydric alcohol, wherein the mass ratio of the polyhydric alcohol to the biomass nanofibers (polyhydric alcohol / biomass nanofibers) is 15 / 85 to 75 / 25.

2. The sheet according to claim 1, further comprising a wet strength agent for paper.

3. The sheet according to claim 2, wherein the wet strength agent for paper is contained in an amount of 0.5 to 15 parts by mass with respect to 100 parts by mass of the biomass nanofibers.

4. The sheet according to claim 1, wherein the viscosity average molecular weight of the biomass nanofibers is 50,000 or more.

5. The sheet according to claim 1, wherein the biomass nanofibers are mechanically defibrated biomass nanofibers.

6. The water content in a moisture absorption environment maintained at 25°C and 85% RH for 3 hours is 15% by mass or more, and / or the water content in a moisture desorption environment maintained at 25°C and 35% RH for 3 hours after being maintained at 25°C and 85% RH for 3 hours is 15% by mass or less. The sheet according to claim 1.

7. The difference between the water content in the moisture absorption environment and the water content in the moisture desorption environment is 10% by mass or more. The sheet according to claim 6.

8. The sheet according to any one of claims 1 to 7, having a tensile strength of 5 MPa or more.

9. A method for manufacturing a sheet, wherein the biomass nanofibers and the polyhydric alcohol are mixed so that the mass ratio of the polyhydric alcohol to the biomass nanofibers (polyhydric alcohol / biomass nanofibers) is 15 / 85 to 75 / 25.

10. A mixed material for manufacturing a sheet, comprising biomass nanofibers and a polyhydric alcohol, wherein the mass ratio of the polyhydric alcohol to the biomass nanofibers (polyhydric alcohol / biomass nanofibers) is 15 / 85 to 75 / 25.

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