Sheet, method for manufacturing the 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 a sheet, and a mixed material.

Background Art

[0002] Hygroscopic and deliquescent materials are utilized in many aspects of daily life because they stabilize the humidity in a space and have a humidity control effect. For example, in clothing applications, sweat and moisture emitted from the human body can cause discomfort such as stuffiness and stickiness. However, by quickly absorbing the moisture inside the clothing and dissipating it to the outside, the comfort during wearing is improved. In addition, in housing applications, by using hygroscopic and deliquescent materials as interior materials of a house, the occurrence of condensation can be prevented, and an environment with a comfortable humidity of 40 to 60% can be maintained for people. Furthermore, in air conditioning equipment, a desiccant air conditioning system that dehumidifies using a drying material is expected to have an energy-saving effect because it consumes less power compared to a conventional dehumidification system using cooling condensation, and applicable hygroscopic and deliquescent materials are required. As described above, materials having both hygroscopicity and deliquescence are required in many fields.

[0003] Examples of materials having both hygroscopicity and deliquescence include silica gel, synthetic zeolite, sodium sulfate, activated alumina, activated carbon, lithium chloride, calcium chloride, magnesium chloride, phosphorus pentoxide, and the like.

[0004] In Patent Document 1, proposals have been made to incorporate the above materials together with pulp or fibers or to form composites into sheets. In addition, in Patent Document 2, a sheet having a hygroscopic and deliquescent function has been proposed by mixing cellulose fibers or kapok fibers, which are hygroscopic and deliquescent materials using natural fibers, with synthetic fibers.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

[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 high-temperature heating is required to remove moisture once it has been absorbed. Furthermore, the sheet described in Patent Document 2 has low moisture absorption and release capacity itself. In other words, none of them can be considered 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 hygroscopic capacity. These polyhydric alcohols are used as raw materials for pharmaceuticals and cosmetics and are commonly used for moisturizing the skin. Polyhydric alcohols are in liquid or powder form and require a suitable binder for molding. While it is possible to mold them in compound form with resin, covering the surface with a hydrophobic resin causes the loss of their original hygroscopic capacity, making it difficult to process sheets that maintain sufficient hygroscopic properties. Furthermore, while these polyhydric alcohols absorb a large absolute amount of moisture when used alone in liquid or powder form, their absorption and release rates are slow, making them time-consuming to use for humidity control purposes. Therefore, they are difficult to use in applications where rapid hygroscopic effects are required.

[0008] Based on the above, the present invention aims to provide a sheet with high hygroscopicity and high moisture release properties after absorption. [Means for solving the problem]

[0009] As a result of diligent research to solve the above problems, the inventors have come up with the present invention described below and found that it can solve the problems. That is, the present invention is as follows.

[0010] [1] 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. [2] The sheet described in [1] further comprising a wet-strengthening agent. [3] The sheet according to [2], comprising 0.5 to 15 parts by mass of the wet-strengthening agent per 100 parts by mass of the biomass nanofiber. [4] The sheet according to any one of [1] to [3], wherein the viscosity-average molecular weight of the biomass nanofiber is 50,000 or more. [5] The sheet according to any one of [1] to [4], wherein the biomass nanofiber is a mechanically defibrated biomass nanofiber. [6] A sheet as described in any one of [1] to [5], wherein the moisture content in a humid environment after being held at 25°C and 85%RH for 3 hours is 15% by mass or more, and / or the moisture content in a humid environment after being held at 25°C and 85%RH for 3 hours and then held at 25°C and 35%RH for 3 hours is 15% by mass or less. [7] The sheet according to [6], wherein the difference between the moisture content under the hygroscopic environment and the moisture content under the hygroscopic environment is 10% by mass or more. [8] A sheet described in 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 polyhydric alcohol such 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 manufacturing 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. [Effects of the Invention]

[0011] According to the present invention, it is possible to provide a sheet with high hygroscopicity and high moisture release properties after absorption. [Brief explanation of the drawing]

[0012] [Figure 1] This is a photograph showing the state without shrinkage, indicating whether or not the sheet can be manufactured according to the example. [Figure 2] This photograph shows the state of minimal shrinkage when determining whether or not the sheet can be manufactured according to the example. [Figure 3] This photograph shows the state of significant shrinkage when determining whether or not the sheet can be manufactured according to the example. [Modes for carrying out the invention]

[0013] The following describes a sheet, a method for manufacturing the sheet, and a mixed material according to one embodiment (this embodiment) of the present invention.

[0014] [Sheet] The sheet according to this embodiment contains biomass nanofibers and polyhydric alcohols, with a mass ratio of biomass nanofibers to polyhydric alcohols (polyhydric alcohol / biomass nanofibers) of 15 / 85 to 75 / 25. By including biomass nanofibers and polyhydric alcohols in the above predetermined ratios, a highly functional moisture-absorbing and releasing sheet can be made that combines the moisture absorption and release rate of biomass nanofibers (especially CNF) and the moisture absorption and release capacity of polyhydric alcohols. In other words, if the mass ratio is less than 15 / 85, the moisture absorption and moisture release after absorption will be low, and if it exceeds 75 / 25, it will be difficult to form a sheet. The mass ratio is preferably 20 / 80 to 75 / 25, and more preferably 25 / 75 to 65 / 35.

[0015] (Biomass nanofibers) Biomass nanofibers can be uniformly dispersed and stabilized in water, and a strong sheet can be obtained by coating and drying. Biomass nanofibers are dispersed in water and have high hydrophilicity, so they can be easily mixed with substances with high affinity for water, such as polyhydric alcohols and wet strength agents. Therefore, a sheet can be easily produced by drying the prepared mixture. Also, by adjusting the concentration and solid content of the dispersion, the sheet thickness can be controlled. Among biomass nanofibers, cellulose in particular is a substance with 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 and reaches equilibrium within 30 minutes in an environment of 20°C and 80% humidity.

[0016] As the biomass nanofibers (BNF) according to this embodiment, they are nanofibers that are biogenic polymers and hardly soluble in water, such as cellulose nanofibers, chitin nanofibers, chitosan nanofibers, silk nanofibers, etc. Among them, cellulose nanofibers (CNF) are 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, further preferably 7 to 50 nm, still further preferably 8 to 25 nm, and particularly preferably 8 to 15 nm. The average length of the biomass nanofibers has a length with an aspect ratio (average length / average fiber diameter) of 10 or more, and is preferably 0.5 to 100 μm, more preferably 10 to 100 μm. The average fiber diameter and average length of the biomass nanofibers can be calculated from the fiber diameter and length (about n = 20) measured based on an electron microscope photograph taken at an appropriate magnification.

[0018] Biomass nanofibers can be produced using various manufacturing methods, including mechanically defibrated biomass nanofibers, and chemically modified biomass nanofibers obtained by chemically treating raw biomass to make it easier to break down, and then further breaking it down mechanically.

[0019] Mechanically defibrated biomass nanofibers, compared to those produced by chemical modification, have fewer impurities because they are formed using only the force of a water jet. Furthermore, they exhibit less reduction in the degree of polymerization and crystallinity from the original raw material compared to chemical modification methods. Additionally, they offer advantages such as fewer processing steps, including the elimination of the need for a washing step after chemical modification.

[0020] The viscosity-average molecular weight of the biomass nanofibers 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. A viscosity-average molecular weight of 50,000 or more improves film formation and allows for the production of sheets without excessive shrinkage or cracking. Among biomass nanofibers, the viscosity-average molecular weight of CNF can be measured by the method described in the examples below. For materials other than CNF, the viscosity-average molecular weight is preferably 50,000 to 150,000 for chitosan nanofibers, and can be measured by dissolving them in a 2% acetic acid / 0.3M sodium chloride aqueous solution. Similarly, 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 to chitosan, and then dissolving it in a 2% acetic acid / 0.3M sodium chloride aqueous solution.

[0021] In the biomass nanofibers according to this embodiment, as previously described, CNF is preferred. This CNF can be produced by known methods such as a method of micronizing cellulose fibers used as raw materials, or a method of synthesis using bacteria such as acetic acid bacteria. Examples of micronizing methods include a method using a water jet, a physical treatment using a defibrillator such as a high-pressure homogenizer (mechanical defibrillation), and a chemical treatment (chemical modification) in which cellulose fibers are loosened by an oxidation reaction using enzymes such as cellulase or catalysts. These treatments can be used in combination.

[0022] Examples of raw cellulose fibers include wood pulp such as coniferous pulp and hardwood pulp, cotton pulp such as cotton linters and cotton lint, and non-wood pulp such as wheat straw, rice straw, rice husks, bagasse, bamboo, agricultural residues (vegetable scraps, tea leaves, mandarin orange peels, etc.), herbaceous plants (such as Japanese pampas grass), and seaweed. These can be used individually or in combination of two or more.

[0023] CNF may be a modified form of cellulose in which the hydroxyl groups of cellulose in the cellulose molecular chain have been altered. Examples of such CNF include those in which the hydroxyl groups of cellulose have been oxidized to carboxyl groups, esterified, or etherified, or in which other functional groups have been introduced to the cellulose fibers. From the viewpoint of improving the dispersibility of CNF, CNF may also be anionically modified CNF, in which anionic groups have been introduced. Examples of anionic groups included in anionically modified CNF include aldehyde groups, carboxyl groups, sulfate groups, and phosphate groups.

[0024] Anionically modified CNF can be obtained by known methods, such as oxidizing the hydroxyl groups of cellulose to convert them into anionic groups, or reacting the hydroxyl groups of cellulose with at least one compound selected from the group consisting of compounds having anionic groups, their acid anhydrides, or derivatives thereof. For example, one method involves using 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO) as a catalyst to react with an oxidizing agent such as sodium hypochlorite and a bromide such as sodium bromide to oxidize the hydroxyl groups of cellulose.

[0025] As the fiber length of CNF increases, the film-forming properties improve; therefore, longer fiber lengths are preferable, and it is preferable to use CNF with long fiber lengths obtained solely by mechanical defibration. Fiber length is correlated with molecular weight (viscosity-average molecular weight), and CNF with a larger viscosity-average molecular weight is preferable.

[0026] (Polyhydric alcohol) Polyhydric alcohols have a strong affinity for water and are hygroscopic. Therefore, by including them in a predetermined ratio along with biomass nanofibers, good hygroscopic properties can be obtained.

[0027] Furthermore, when biomass nanofibers alone are heated and dried to produce a sheet, 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 it by applying pressure from above using special equipment. In addition, a major problem with sheets made solely from biomass nanofibers was their lack of flexibility. In contrast, in this embodiment, by adding polyhydric alcohols, plasticity is imparted to the biomass nanofibers, allowing for the production of a smooth and flexible sheet without shrinkage through simple heat drying alone.

[0028] In this embodiment, polyhydric alcohol means alcohol with a hydrity of 2 or more, and examples include dihydric alcohols, trihydric alcohols, tetrahydric alcohols, pentahydric alcohols, hexahydric or higher alcohols, and ethers thereof, with the preference being an alcohol with a hydrity of 3 or more, or a polyether of a dihydric alcohol.

[0029] Examples of dihydric alcohols include C2-C6 chain hydrocarbon diols, such as C2-C6 glycols, such as ethylene glycol, propylene glycol, dipropylene glycol, 1,3-butanediol, isoprene glycol, pentylene glycol, or hexylene glycol. Examples of trihydric alcohols include the aforementioned chain-like hydrocarbon triols, such as glycerin. Examples of the tetrahydric alcohols mentioned above include the chain-like hydrocarbon tetraols described above, such as pentaerythritol. Examples of alcohols with a valency of 5 or higher include xylitol and sorbitol. Examples of the above-mentioned ethers include diethylene glycol, dipropylene glycol, diglycerin, triethylene glycol, tripropylene glycol, tetraethylene glycol, and tetrapropylene glycol.

[0030] From the viewpoint of hygroscopic capacity, the polyhydric alcohol in this 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 fluctuates depending on the relative humidity of the environment. For example, glycerin reaches a moisture content of over 50% after 4 days of standing at 20°C and 80% humidity, indicating a very large absolute amount of moisture absorption. However, the moisture content after 1 hour at 20°C and 80% humidity is only about 1.5%, and the rate of moisture absorption may be slow. But when biomass nanofibers are present, the rate of moisture absorption increases, resulting in good moisture absorption and release properties as a sheet.

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

[0033] The wet-strength agent in this embodiment is not particularly limited and includes, for example, urea-formaldehyde resin, melamine-formaldehyde resin, polyamide-polyamine-epichlorohydrin resin, polyamide-epoxy resin, plant-based gum, latex, polyethyleneimine, and the like. Among these, polyamide-epoxy resin is preferred. In addition to the wet strength agent, paper strength enhancers such as glyoxal, gum, mannogalactan polyethyleneimine, polyacrylamide resin, polyvinyl alcohol, starch, carboxymethylcellulose, guar gum, and urea resin may be used.

[0034] The amount of wet-strengthening agent is preferably 0.5 to 15 parts by mass, and more preferably 0.8 to 13 parts by mass, per 100 parts by mass of biomass nanofiber. A concentration of 0.5 to 15 parts by mass provides good water resistance and prevents the sheet from becoming too rigid.

[0035] In the sheet according to this embodiment, the total amount of biomass nanofibers and 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, from the viewpoint of more reliably exhibiting the effects of the present invention. Other components besides biomass nanofibers and polyhydric alcohols include the aforementioned wet-strengthening agents, but other components such as polyvinyl alcohol (PVA) may also be included.

[0036] The polyvinyl alcohol is not particularly limited, and known types can be used. Furthermore, it is produced by polymerizing vinyl esters using known methods such as solution polymerization, bulk polymerization, and suspension polymerization to obtain a polymer, and then saponifying the polymer. Only one type of polyvinyl alcohol may be used, or two or more types may be used in combination.

[0037] Examples of vinyl esters mentioned above include vinyl acetate, vinyl formate, vinyl propionate, vinyl butyrate, vinyl pivalate, vinyl versaticate, vinyl laurate, vinyl stearate, and vinyl benzoate.

[0038] The degree of polymerization of polyvinyl alcohol is not particularly limited and can be any within the range of commercially available products. For example, a degree of polymerization of 100 to 4000 is preferred, 100 to 2000 is more preferred, and 100 to 1000 is even more preferred. Furthermore, the degree of saponification of the polyvinyl alcohol is preferably 80 mol% or higher, and more preferably 90 mol% or higher. The degree of polymerization of polyvinyl alcohol can be measured by solution viscosity measurement in accordance with JIS K6726:1994 (Test Methods for Polyvinyl Alcohol). The degree of saponification can be determined in accordance with JIS K 6726:1994.

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

[0040] In the sheet according to this embodiment, polyvinyl alcohol is preferably present in an amount of 30% by mass or less, more preferably in an amount of 5 to 25% by mass, and even more preferably in an amount of 7 to 20% by mass.

[0041] (Physical properties) The sheet according to this embodiment preferably has a moisture content of 15% by mass or more in a humid environment after being held at 25°C and 85% RH for 3 hours (hereinafter sometimes referred to as "humid environment moisture content"), and / or a moisture content of 15% by mass or less in a humid environment after being held at 25°C and 85% RH for 3 hours and then held at 25°C and 35% RH for 3 hours (hereinafter sometimes referred to as "humid environment moisture content"). This allows the sheet to quickly respond to changes in ambient humidity by absorbing and releasing moisture.

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

[0043] Furthermore, the difference between the moisture content of the humidifying environment and the moisture content of the humidifying environment is preferably 10% by mass or more, preferably 15% by mass or more, and the upper limit is practically around 50% by mass. A difference of 10% by mass or more allows for rapid response to changes in ambient humidity, enabling moisture absorption and release.

[0044] The sheet according to this embodiment preferably has a tensile strength of 5 MPa or more, more preferably 6 MPa or more, and even more preferably 10 MPa or more. A tensile strength of 5 MPa or more provides a sheet with excellent strength and ease of handling. While there is no particular upper limit to the preferred tensile strength, in practice it is around 100 MPa.

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

[0046] The sheet according to this embodiment can be subjected to known processing, lamination, composite formation, etc., as needed, and applied to applications such as various clothing items, interior materials for living spaces, moisture absorption and release members used in air conditioning systems, and moisture-sensing films for humidity sensors.

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

[0048] Specifically, the solid components after drying are weighed to obtain a predetermined mass ratio of biomass nanofibers, polyhydric alcohol, and an optional wet-strengthening agent, and then mixed using a rotation-and-revolution mixer at a rotational speed of 1000-2000 min⁻¹. -1 The mixture is stirred and mixed for 3 to 30 minutes under conditions where the rotation speed is 50% of the orbital speed. If bubble removal is necessary, it is preferable to perform the stirring process under vacuum. After that, the mixture is placed in a designated container and dried to produce a sheet. Drying is preferably carried out at 40 to 70°C for about 1 to 3 days.

[0049] [Mixed material] The mixed material for the sheet according to this embodiment is a mixed material for manufacturing a sheet, comprising biomass nanofibers and polyhydric alcohols, wherein the mass ratio of biomass nanofibers to polyhydric alcohols (polyhydric alcohol / biomass nanofibers) is 15 / 85 to 75 / 25.

[0050] By including biomass nanofibers and polyhydric alcohols in the aforementioned proportions, a highly functional moisture-absorbing and releasing sheet material can be created that combines the moisture absorption and release rate of biomass nanofibers (especially CNF) with the moisture absorption and release capacity of polyhydric alcohols.

[0051] Details of biomass nanofibers, polyhydric alcohols, etc., are as described in the sheet of this embodiment. Similarly, when including wet-strengthening agents, polyvinyl alcohol, etc., the details are as described in the sheet of this embodiment. [Examples]

[0052] [Example 1] 5 wt% BiNFi-s RMa (manufactured by Sugino Machine, model: RMa-10005, viscosity-average molecular weight 124,000, average fiber diameter 10 nm) was used as the CNF. Glycerin was manufactured by Fujifilm Wako Pure Chemical Industries, and polyamide epoxy resin (manufactured by Taoka Chemical Industries, model: Sumirez Resin 675A) was used as the wetting strength agent. After drying, the solids were weighed so that the mass ratio was CNF:glycerin:wetting force agent = 80:20:1. The mixture was then stirred and mixed for 10 minutes in a rotary-orbit mixer (Hymerger, Kyoritsu Seiki, HM-200WV) at a setting of 9 with vacuum to prepare the 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.

[0053] [Examples 2-10, Comparative Examples 1-4] A mixed material was prepared in the same manner as in Example 1, except that the mass ratio of CNF:glycerin:wetting force agent was changed as shown in Tables 1 and 2, and a sheet was then prepared. Furthermore, it was not possible to produce sheets using Comparative Examples 3 and 4.

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

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

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

[0057] [Example 14] A mixed material was prepared in the same manner as in Example 1, except that 5 wt% BiNFi-s WFo (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:wetting force agent was changed as shown in Table 2. A sheet was then prepared.

[0058] [Example 15] A mixed material was prepared in the same manner as in Example 1, except that Rheocrysta (I-2SX, manufactured by Daiichi Kogyo Seiyaku, average fiber diameter 3 nm), an anionic modified CNF, was used instead of 5 wt% BiNFi-s RMa as the CNF, and the mass ratio of CNF:glycerin:wetting force agent was changed as shown in Table 2. A sheet was then prepared.

[0059] [Examples 16-19] 5 wt% BiNFi-s RMa (manufactured by Sugino Machine, model: RMa-10005, viscosity-average molecular weight 124,000, average fiber diameter 10 nm) was used as CNF. Glycerin was manufactured by Fujifilm Wako Pure Chemical Industries, and polyamide epoxy resin (manufactured by Taoka Chemical Industries, model: Sumirez Resin 675A) was used as the wetting agent. Polyvinyl alcohol (PVA) manufactured by Fujifilm Wako Pure Chemical Industries (degree of polymerization: 1500-1800, fully saponified type) was used. After drying, the mass ratio of CNF:glycerin:wetting force agent:PVA was weighed as shown in Table 2, and the mixed material was prepared by stirring and mixing for 10 minutes in a rotary-orbit mixer, Hymerger (HM-200WV, manufactured by Kyoritsu Seiki), under conditions of setting value 9 and vacuum. 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 using the viscosity method. Specifically, a dry powder sample was obtained by freeze-drying an aqueous dispersion of CNF. Then, samples of each cellulose fiber were dissolved in a copper ethylenediamine solution, and the intrinsic viscosity was determined from the relative viscosity of the solution to the solvent using an Ostwald viscometer, thereby calculating the molecular weight (viscosity-average molecular weight) of each cellulose fiber.

[0061] <Feasibility of sheet creation> The shape of the sheets obtained in each example was visually inspected using a ruler and classified into the following four stages. The results are shown in Tables 1 and 2. No shrinkage: ◎, Little shrinkage: ○, Large shrinkage: △, Cannot be made into a sheet: × In addition, "no shrinkage" refers to a state where more than 90% of the sheet is smooth and there are almost no irregularities, as shown in Figure 1. "Slight shrinkage" refers to a state where more than 80% of the sheet is smooth and there are irregularities in less than 20%, as shown in Figure 2. "Large shrinkage" refers to a state where more than 20% of the sheet has irregularities, as shown in Figure 3.

[0062] <Evaluation of moisture absorption and release properties> Test specimens were prepared by cutting the sheets obtained in each example to a size of 20 mm x 20 mm. The test specimens were heated and dried at 105°C for 2 hours, and their weight was measured in an extremely dry state. After that, they were pre-conditioned in an environment of 25°C and 35% RH humidity. Next, moisture absorption and release tests of the sheet material were conducted using a constant temperature and humidity chamber (ESPEC, model: PSL-2J) under specified temperature and humidity conditions. First, the sheets were placed in an environment of 25°C and 85% RH humidity, and the weight change after 3 hours was recorded to evaluate the moisture absorption characteristics of the sheets. Next, the sheets were placed in an environment of 25°C and 35% RH humidity, and the moisture release characteristics of the sheets 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, dumbbell-shaped test specimens of type 8 were cut out, and the sheet thickness was measured. Then, after standing for 3 hours in a dry environment (25°C, 35%RH) and a humid environment (25°C, 70%RH), tensile tests were performed. The tensile tests were conducted at 25°C using a precision universal testing apparatus (Shimadzu Corporation, model: AG-50KNXD), and the tensile strength and strain (elongation) were measured. The test conditions were set to a test speed of 2 mm / min and a grip distance of 30 mm. The results are shown in Tables 1 and 2. In Comparative Examples 1 and 2, the shrinkage was too great, leaving no space to cut out tensile test specimens, and therefore measurement was not possible.

[0064] [Table 1]

[0065] [Table 2]

Claims

1. A sheet containing biomass nanofibers and polyhydric alcohols, The mass ratio of the biomass nanofiber to the polyhydric alcohol (polyhydric alcohol / biomass nanofiber) is 15 / 85 to 75 / 25. The aforementioned polyhydric alcohol is any of a dihydric alcohol, trihydric alcohol, tetrahydric alcohol, pentahydric alcohol, or an ether thereof. The viscosity-average molecular weight of the biomass nanofiber is 50,000 or more. A sheet in which the biomass nanofibers are cellulose nanofibers.

2. Furthermore, the sheet according to claim 1, further comprising a wet-strengthening agent.

3. The sheet according to claim 2, wherein the wet-strengthening agent is contained in an amount of 0.5 to 15 parts by mass per 100 parts by mass of the biomass nanofiber.

4. The sheet according to any one of claims 1 to 3, wherein the biomass nanofibers are mechanically defibrated biomass nanofibers.

5. A sheet according to any one of claims 1 to 3, wherein the moisture content in a humid environment maintained at 25°C and 85% RH for 3 hours is 15% by mass or more, and / or the moisture content in a humid environment maintained at 25°C and 85% RH for 3 hours, followed by 3 hours at 25°C and 35% RH, is 15% by mass or less.

6. The sheet according to claim 5, wherein the difference between the moisture content under the hygroscopic environment and the moisture content under the hygroscopic environment is 10% by mass or more.

7. A sheet according to any one of Claims 1 to 3, wherein after cutting out a dumbbell-shaped test piece of type 8, it is left to stand for 3 hours in a dry environment (25°C, 35% RH) and a humid environment (25°C, 70% RH), and then a tensile test is performed at 25°C using a precision universal testing apparatus (test speed 2 mm / min, grip distance 30 mm), and the tensile strength obtained is 5 MPa or more.

8. A method for manufacturing a sheet, comprising mixing biomass nanofibers and polyhydric alcohol such that the mass ratio of the biomass nanofibers to the polyhydric alcohol (polyhydric alcohol / biomass nanofibers) is 15 / 85 to 75 / 25, The aforementioned polyhydric alcohol is any of a dihydric alcohol, trihydric alcohol, tetrahydric alcohol, pentahydric alcohol, or an ether thereof. The viscosity-average molecular weight of the biomass nanofiber is 50,000 or more. A method for producing a sheet in which the biomass nanofiber is a cellulose nanofiber.

9. A mixed material for manufacturing a sheet, It contains biomass nanofibers and polyhydric alcohols. The mass ratio of the biomass nanofiber to the polyhydric alcohol (polyhydric alcohol / biomass nanofiber) is 15 / 85 to 75 / 25. The aforementioned polyhydric alcohol is any of a dihydric alcohol, trihydric alcohol, tetrahydric alcohol, pentahydric alcohol, or an ether thereof. The viscosity-average molecular weight of the biomass nanofiber is 50,000 or more. A mixed material in which the biomass nanofibers are cellulose nanofibers.

Images